- 8 tablespoons (1 stick) butter, divided
- 2 large sweet onions, sliced
- 2 pounds ground beef
- 2 tablespoons beef base (such as Better than Boullion), divided
- 1 tablespoon Worcestershire sauce, divided
- Kosher salt and black pepper, to taste
- 24 slider buns
- 12–16 ounces gruyere or swiss cheese, shredded
- 2 tablespoons sesame seeds
- 1 tablespoon fresh thyme
- 1 teaspoon onion powder
- 1 teaspoon garlic powder
- Melt 2 tablespoons of the butter in a skillet over medium heat. Add in the onions and reduce the heat to medium low. Cook, stirring occasionally, until lightly caramelized, about 25-30 minutes. If the onions start to look dry or burnt, add a tablespoon of water to the pan.
- In a large bowl, mix the ground beef with half of the beef base and half of the Worcestershire sauce. Season with salt and pepper.
- Add the beef to the skillet full of onions. Increase heat to medium-high and brown the beef, breaking it up and mixing with the onions as you go. Once browned, drain off excess grease.
- Preheat the oven to 350°F. Lightly grease a large baking sheet. Separate the tops from the bottoms of the slider buns. Fit the slider bottom buns tightly on the baking sheet.
- Evenly distribute the beef and onion mixture over the bottom buns. Top with the gruyere cheese. Cover with the top buns.
- In a microwave safe bowl, melt the butter with the remaining beef base. Stir in the remaining Worcestershire sauce and continue to mix until well-combined. Using a pastry brush, brush the beefy butter mixture over the top buns. Sprinkle with the sesame seeds, thyme, onion powder, and garlic powder.
- Bake the sliders until the cheese is fully melted and the tops of the rolls are lightly browned, about 20 minutes.