2 pounds 80/20 ground beef
1 medium yellow onion, minced
1 24-pack sweet Hawaiian rolls
16 slices American cheese
¼ cup tomato ketchup
¼ cup yellow mustard
2 tablespoons butter, melted
Kosher salt and freshly ground black pepper
Preheat oven to 350 F. Spray a 9-by-13-inch baking pan with cooking spray.
Heat a skillet over medium heat. Add the onions and ground beef together, and start breaking up the meat with a spatula.
Cook until the beef is completely browned and the onions are soft and translucent. Season with salt and pepper to taste, and set aside to cool.
Split the sweet rolls lengthwise using a serrated knife. Fit the bottom half of the rolls snugly in the presprayed baking dish.
Place 8 cheese slices across the bottom of the rolls.
Carefully spoon the meat mixture over the cheese across the entire casserole dish.
Drizzle the ketchup and mustard over the meat, and layer with the remaining 8 cheese slices. Top the casserole with the tops of the Hawaiian sweet rolls.
Brush tops of the rolls with melted butter, and cover the whole dish with aluminum foil.
Bake the casserole, covered, for 30 minutes, then remove the foil, and allow to cook for another 15-20 minutes. Cooking is done with the roll tops are golden brown and the cheese is melted.
Remove the casserole dish from the oven, and allow to cool for 10 minutes. If the dish is still warm, serve individual sliders using a spatula. Once the dish is cooled, you can use your hands to rip them apart!
Pro-tip: Have extra toppings available by the time you're ready to eat. Load on some extra fresh-chopped onion or green relish for more flavor.
Pro-tip: These sliders are served best with easy sides like potato chips or French fries.
