Cheeseburger sliders

2 pounds ground beef
1/2 cup chopped onion
8 slices cheddar cheese
6 ounces shredded cheddar cheese
24 dinner rolls
2 tablespoons butter

Preheat oven to 350 degrees. Butter the bottom of rimmed baking sheet. Brown hamburger in skillet and add onion, then remove from heat. Cut buns in half and place all the bottoms on buttered baking sheet. Place sliced cheese on the buns, then spread the ground beef evenly over the cheese layer. Sprinkle the shredded cheese on top of the meat layer. Place the tops of the buns on top and brush the melted butter on top. Bake for 12-15 minutes until cheese is melted and tops are browned.