If you're craving the ultimate comfort bite, this Buttery Roast Beef Sliders with Caramelized Onions Recipe is where your kitchen adventure begins. Imagine tender roast beef, sweet caramelized onions, and melty cheese all hugged by soft, buttery Hawaiian rolls—pure bliss in every bite.

The image shows a close-up of two stacked sandwiches on a wooden board. Each sandwich has three main layers: the top and bottom are golden brown toasted buns sprinkled with sesame seeds and seasoning, the middle layer is melted light yellow cheese with caramelized onions that are juicy and golden, and there is a layer of thin slices of cooked meat underneath the cheese. Some melted cheese and onions are dripping out from the sides, making the sandwich look rich and full. The background is dark, and the wood texture underneath contrasts with the food. photo taken with an iphone --ar 2:3 --v 7

Jump to:

Why You'll Love This Recipe
Ingredients & Why They Work
Make It Your Way
Step-by-Step: How I Make Buttery Roast Beef Sliders with Caramelized Onions Recipe
Top Tip
How to Serve Buttery Roast Beef Sliders with Caramelized Onions Recipe
Make Ahead and Storage
Frequently Asked Questions:
Final Thoughts
Buttery Roast Beef Sliders with Caramelized Onions Recipe

Why You'll Love This Recipe

I’m absolutely obsessed with how these sliders come together. Every element adds a layer of flavor, and they’re honestly one of my go-to recipes when I want to wow guests or just treat myself to something extra special at home.

Perfect party food: These sliders are easy to make in batches and always disappear fast.
Rich, savory flavors: The caramelized onions and au jus bring depth that elevates simple roast beef.
Soft, buttery buns: Hawaiian rolls brushed with garlic butter give a sweet, melt-in-your-mouth touch.
Homemade garlic aioli: Adds creaminess and a bright punch that pairs beautifully with the beef.

Ingredients & Why They Work

Before you dive in, here’s a quick rundown of the key ingredients to look for. Picking the right components makes a big difference in bringing out those rich, buttery, and savory flavors.

Flat lay of a cluster of 3 large yellow onions, thinly sliced in a small white ceramic bowl, a small white bowl of unsalted butter cubes, a small white bowl with olive oil, a small white bowl of light olive oil, a clean large whole brown egg with uncracked shell, a small white bowl with Dijon mustard, a single fresh garlic clove, a small white bowl of fresh lemon juice, a small white bowl with kosher salt, a small white bowl with brown sugar, a small white bowl with finely shredded mozzarella cheese, a stack of thinly sliced deli roast beef, a neat pile of sliced provolone cheese, a cluster of 12 Hawaiian slider buns halved horizontally, a small white bowl with Worcestershire sauce, a small white bowl with poppy seeds, a small white bowl with white sesame seeds, a small white bowl with garlic powder, a small white bowl with dried minced onion, a small white bowl of freshly cracked black pepper, all arranged symmetrically on a clean white marble surface, soft natural light, photo taken with an iPhone, professional food photography style, fresh ingredients, white ceramic bowls, no bottles, no duplicates, no utensils, no packaging --ar 2:3 --v 7 --p m7354615311229779997

Unsalted butter: Crucial for controlling saltiness and creating that luscious garlic butter sauce soaking the tops of the buns.
Olive oil: Used alongside butter to cook the onions gently without burning, helping them turn golden and jammy.
Yellow onions: Their natural sweetness intensifies as they caramelize, giving the sliders that irresistible depth.
Kosher salt: Helps season throughout and balance the sweetness from onions and buns.
Brown sugar: Speeds up caramelization and adds a subtle molasses note without overpowering.
Beef broth: Used twice—once to deglaze the onions and again for the au jus, infusing that deep meaty flavor.
Egg yolk: The base for homemade garlic aioli, creating a creamy richness you won’t want to skip.
Dijon mustard & garlic: Bring a zesty, garlicky kick to the aioli, making each bite pop.
Lemon juice: Adds brightness and balances the richness of the aioli and buttered buns.
Light olive or neutral oil: Helps emulsify the aioli without overpowering flavor.
Better than Bouillon Beef Base: Concentrated beef flavor that makes the au jus deeply savory and satisfying.
Worcestershire sauce: Adds umami complexity both in the au jus and garlic butter sauce.
Slider buns (Hawaiian rolls preferred): Soft, slightly sweet, and perfect for soaking up juices without falling apart.
Deli roast beef: Choose thin slices for layering, tender texture, and true beefy flavor.
Melty cheese (provolone, Swiss, or muenster): Adds gooey layers that marry all the flavors.
Shredded mozzarella: Sprinkled on top for extra cheesy goodness.
Poppy seeds & white sesame seeds: Give a delightful crunch and a hint of nuttiness to the garlic butter topping.
Garlic powder & dried minced onion: Enhance the savory garlic butter sauce brushed over the buns.
Freshly cracked black pepper: Finishes the sliders with just the right touch of spice.

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Note: You'll find the complete list of ingredients, along with their exact measurements, in the printable recipe card at the bottom of this post.

Make It Your Way

Feel free to customize these buttery roast beef sliders to match your taste or occasion. Whether you want to lighten them up, add some extra zing, or switch up the bread, there’s plenty of room to make this recipe your own.

Vegetarian Variation: Swap the roast beef for thick slices of grilled portobello mushrooms or a roasted veggie medley. The caramelized onions and garlic aioli still shine, making these sliders satisfyingly savory even without meat.
Cheese Options: I love how provolone melts beautifully here, but Swiss or muenster add great flavor twists. For an extra creamy texture, sprinkle shredded mozzarella on top, just like the original recipe suggests!
Quick Version: When time’s tight, I whip up a faster 30-minute version by using mayonnaise spiked with garlic, mustard, and lemon instead of the homemade aioli—and skipping the caramelized onions. Still delicious and way quicker!
Bread Choices: Hawaiian rolls are soft, sweet, and perfect for soaking up that garlicky butter, but feel free to try your favorite slider buns or even small brioche buns. Each brings its own character to the sliders.
Spice it Up: Want a little heat? Add a dash of cayenne or some sliced pickled jalapeños atop the caramelized onions for a spicy kick that pairs beautifully with the rich beef and cheese.

Step-by-Step: How I Make Buttery Roast Beef Sliders with Caramelized Onions Recipe

A woman's hand is holding a sandwich made with a toasted, golden-brown sesame seed bun, dripping with thick brown gravy. Inside the sandwich, there are multiple layers of soft, thin slices of cooked meat and melted cheese with a creamy texture, visible just under the bun. Below the sandwich, a white bowl filled with rich brown gravy has some gravy dripping down its side onto a dark wooden surface. Behind the bowl, several more sandwiches with the same sesame seed buns, meat, and cheese are stacked, showing their melted cheese and crispy textures. The whole scene is set on a white marbled surface with a blurred dark shirt in the background, capturing the warm, messy, and inviting aspect of the dish. photo taken with an iphone --ar 2:3 --v 7

Step 1: Slow-Cook Those Onions to Golden Perfection

Start by melting butter and olive oil in a large skillet over medium-low heat. Add your thinly sliced yellow onions, sprinkle on salt and brown sugar, and let them cook low and slow. Stir occasionally, and watch as the onions gradually soften and deepen to a rich golden brown, about 45 minutes. Be patient—this slow caramelization is what gives the onions that irresistibly sweet, jammy flavor. When the onions are beautifully caramelized, stir in beef broth to deglaze the pan, scraping up all the flavorful bits. Set them aside while you move on to the next step.

Step 2: Whip Up Creamy Homemade Garlic Aioli

In a small bowl, whisk together the egg yolk, Dijon mustard, grated garlic, and fresh lemon juice until smooth and bright. Using an immersion blender or a trusty whisk, slowly drizzle in the light olive oil while blending to build a luscious, creamy aioli. It should thicken to silky perfection—season with kosher salt to taste, then set this garlicky goodness aside. If you’re short on time, feel free to stir these flavors into mayonnaise to mimic the aioli.

Step 3: Simmer a Rich, Flavorful Au Jus Sauce

For that classic dip, melt butter in a medium saucepan over medium heat. Add Better than Bouillon beef base, beef broth, and Worcestershire sauce, then let everything simmer gently for 20 minutes until the mixture reduces by half, thickens slightly, and deepens in color. Keep this au jus warm so it’s ready for dipping once the sliders come out of the oven.

Step 4: Toast the Bottom Buns Just Right

Preheat your oven to 350°F (180°C). Slice your slider rolls in half horizontally, but keep them together so they don’t separate. Arrange the bottom halves cut-side up on a parchment-lined baking sheet. Lightly brush them with melted butter or a bit of your homemade aioli to add extra flavor and help them toast beautifully. Bake for 5 minutes until tender and golden—perfect for holding all those delicious toppings without getting soggy.

Step 5: Layer Up the Deliciousness

Spread a generous layer of the garlic aioli over each toasted bottom bun—this is where the flavor party starts. Pile on the roast beef in 2 to 3 layers to make every bite satisfying. Next, lay slices of your melty cheese choice, then sprinkle shredded mozzarella on top for that ooey-gooey texture. Finish each slider with a hearty spoonful of the golden caramelized onions you made earlier.

Step 6: Top Off and Brush with Garlic Butter Magic

Pop on the top halves of your rolls. In a small bowl, combine melted butter with Worcestershire sauce, poppy seeds, white sesame seeds, garlic powder, dried minced onion, kosher salt, and freshly cracked black pepper. Brush this flavorful garlic butter generously over the tops of your sliders—this step locks in moisture and adds a gorgeous golden crust once baked.

Step 7: Bake to Melty, Golden Glory

Cover the sliders loosely with foil to keep them moist, then bake for 10 minutes. Remove the foil and bake for another 10 minutes, or until the tops turn golden brown and the cheese melts into all those layers beneath. The kitchen will smell heavenly!

Step 8: Slice, Serve, and Dip!

Carefully slice between each slider to separate them. Serve warm with little bowls of your homemade au jus sauce on the side for dipping. The combination of juicy roast beef, melted cheese, caramelized onions, and garlicky butter together with the savory au jus is absolutely irresistible.

Top Tip

These tips come straight from my kitchen experiments, helping you nail the perfect Buttery Roast Beef Sliders with Caramelized Onions every time without the guesswork.

Slow-Caramelized Onions: Patience is key! Cooking your onions low and slow for the full 45 minutes really brings out that deep, jammy sweetness that sets these sliders apart.
Garlic Aioli Shortcut: If you’re short on time, mixing garlic, Dijon, lemon, and salt into mayonnaise is a lifesaver and still delivers big flavor.
Butter Brush Magic: Don’t skimp on brushing the tops of your buns with the garlic butter mix — it’s what gives these sliders that golden, flavorful crust that’s irresistible.
Watch the Bake Time: Covering the sliders with foil for the first 10 minutes keeps them from drying out, and finishing uncovered melts the cheese perfectly without burning the tops.

How to Serve Buttery Roast Beef Sliders with Caramelized Onions Recipe

A tan baking tray holds five slices of light yellow bread with a soft texture. Each slice is spread with a layer of creamy white mayonnaise, which is smooth with small bits of green herbs mixed in. The slices are arranged close together, with three on the bottom and two on the top, placed on a white marbled surface. Photo taken with an iphone --ar 2:3 --v 7

Garnishes

To elevate these sliders even further, try topping them with fresh arugula or a sprinkle of chopped fresh parsley for a pop of color and peppery brightness. A few pickled jalapeño slices add a pleasant tangy heat that pairs beautifully with the rich roast beef.

Side Dishes

These sliders pair wonderfully with classic sides like crispy sweet potato fries, crunchy dill pickle spears, or a tangy coleslaw to balance the buttery richness. You could also serve a light mixed greens salad with a vinaigrette to keep things fresh and vibrant.

Make Ahead and Storage

Storing Leftovers

Store your leftover Buttery Roast Beef Sliders in an airtight container in the refrigerator for up to 3 days. This keeps the flavors intact and prevents the buns from drying out.

Freezing

If you'd like to freeze them, assemble the sliders without the caramelized onions and garlic butter topping first. Wrap each slider tightly in plastic wrap and place in a freezer-safe bag. Freeze for up to one month. When ready, thaw in the fridge overnight before adding onions and butter, then bake as directed.

Reheating

Reheat leftovers in the oven at 375°F for about 10 minutes. This method warms them through evenly and helps keep the buns from turning soggy. Avoid microwaving if possible, as it tends to make the bread chewy.

Frequently Asked Questions:

Can I use store-bought caramelized onions instead of making my own?

Absolutely! While homemade caramelized onions have unbeatable flavor, using pre-made ones can save time and still add delicious sweetness to your sliders.

What type of cheese melts best for these sliders?

Provolone, Swiss, or muenster are all excellent choices because they melt smoothly and complement the savory beef without overpowering the flavors.

Is it safe to eat homemade aioli made with raw egg yolk?

If you’re concerned about raw eggs, you can use pasteurized eggs or substitute with mayonnaise mixed with garlic and lemon for a similar flavor without the risk.

Can these sliders be made ahead for a party?

Yes! You can assemble the sliders up to two days in advance without the caramelized onions and garlic butter topping. Then add those and bake them just before serving for freshness.

Final Thoughts

There’s something so comforting about buttery, melty roast beef sliders, especially when you add that deep sweetness from caramelized onions and the zing of homemade garlic aioli. Whether it’s game day, a family gathering, or a cozy weeknight treat, these sliders bring a warmth and joy that’s hard to beat. I hope you enjoy making and sharing this Buttery Roast Beef Sliders with Caramelized Onions Recipe as much as I do—bon appétit!