Instructions

• Heat the oven to 350°F. Line a 9-by-13-inch baking dish with parchment, leaving enough overhang to lift the sliders out later.
• Cook the diced onion in a skillet over medium heat until softened, about 4 minutes. Add the ground beef, salt, pepper, and garlic powder; cook until browned and no pink remains, breaking the meat into small crumbles. Drain excess fat if needed.
• Slice the buns as one connected slab. Place the bottom half in the prepared dish and spread the cooked beef evenly over it.
• Cover the beef with the cheese slices, add pickles if using, and set the top bun slab over the filling.
• Brush the tops with melted butter and sprinkle with sesame seeds if using. Cover loosely with foil and bake for 15 minutes.
• Remove the foil and bake for 5 to 8 minutes more, until the cheese is fully melted and the bun tops are lightly golden. Rest for 5 minutes, then separate and serve.