Preheat the oven to 350°F and line a large sheet pan or two 9x13-inch baking dishes with foil.

Brown the ground beef and onion together in a large skillet over medium-high heat for 8 minutes, until no pink remains in the meat.

Drain off excess grease, then add the garlic and cook for 1 minute.

Stir in the ketchup, brown sugar, Worcestershire sauce, mustard, tomato paste, salt and pepper.

Simmer uncovered for 8 to 10 minutes, stirring often, until the mixture thickens enough to coat the back of a spoon and hold its shape on a bun.

Slice the slider buns in half as a block, keeping the tops and bottoms connected, and set the bottoms in the prepared pan.

Spread the sloppy joe mixture evenly over the bottom buns, then cap with the top half.

Brush the tops with melted butter and bake for 8 to 10 minutes, until the buns are warmed through and lightly toasted.

Slice into individual sliders and serve warm, straight from the pan.