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French Onion Beef Sliders - Savory, Melty, Crowd-Pleasing Mini Sandwiches

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Prep Time 15 minutes
Cook Time 35 minutes
Total Time 50 minutes
Servings: 12 servings
Ingredients Method

Ingredients
  

  • 12 slider buns (Hawaiian or brioche-style)
  • 1.25–1.5 pounds ground beef (80/20 for juiciness)
  • 3 large yellow onions, thinly sliced
  • 2 tablespoons unsalted butter (for onions)
  • 1 tablespoon olive oil (for onions)
  • 1 teaspoon kosher salt, plus more to taste
  • 1/2 teaspoon black pepper, plus more to taste
  • 1 teaspoon fresh thyme leaves (or 1/2 teaspoon dried)
  • 2 cloves garlic, minced
  • 1 tablespoon Worcestershire sauce
  • 1/2 cup beef stock (low sodium)
  • 8 ounces Gruyère, shredded (or Swiss/provolone mix)
  • 4 ounces provolone, sliced (optional, for extra melt)
  • 2 tablespoons Dijon mustard
  • 2 tablespoons mayonnaise (optional, for a creamy spread)
  • 2 tablespoons unsalted butter (for topping)
  • 1/2 teaspoon garlic powder
  • 1 teaspoon poppy seeds (optional)
  • Fresh parsley, minced (optional, for garnish)

Method
 

  1. Caramelize the onions. In a large skillet, warm 2 tablespoons butter and 1 tablespoon olive oil over medium heat. Add the sliced onions, 1 teaspoon salt, and a pinch of pepper. Cook, stirring periodically, for 25–35 minutes until deep golden and jammy. If the pan dries, add a splash of water to deglaze.
  2. Add aromatics. Stir in the garlic and thyme. Cook 1–2 minutes until fragrant. Remove half the onions to a bowl to use later on top of the sliders.
  3. Brown the beef. Push remaining onions to one side of the pan. Add ground beef to the open side, season with a pinch of salt and pepper, and cook over medium-high heat, breaking it up until browned and mostly cooked through, about 5–7 minutes. Mix onions and beef together.
  4. Build the French onion flavor. Stir in Worcestershire and beef stock. Simmer 2–3 minutes until most of the liquid reduces but the mixture is still juicy, not dry. Taste and adjust salt and pepper.
  5. Prep the buns and oven. Heat oven to 350°F (175°C). Line a 9x13-inch baking dish or sheet pan with parchment. Slice the slider buns horizontally, keeping the top and bottom slabs intact.
  6. Make the spread. In a small bowl, combine Dijon and mayonnaise. Spread on the cut side of the bottom buns. This adds moisture and tang.
  7. Layer the cheese. Sprinkle half the Gruyère over the bottom buns. This creates a barrier to keep the buns from getting soggy.
  8. Add the beef mixture. Spoon the beef-onion mixture evenly over the cheese. Top with the reserved caramelized onions for extra sweetness and texture.
  9. Finish with more cheese. Add the remaining Gruyère and the provolone slices, if using. Place the top buns on.
  10. Brush with garlic butter. Melt 2 tablespoons butter with garlic powder. Brush over the tops of the buns and sprinkle with poppy seeds.
  11. Bake. Cover loosely with foil and bake for 12–15 minutes, until the cheese is melted. Uncover and bake 5 more minutes to lightly toast the tops.
  12. Rest and slice. Let the sliders rest 3–5 minutes. Use a serrated knife to cut along the bun lines. Garnish with parsley and serve warm.