Ingredients

• 2 tbsp. mayonnaise
• 4 tsp. ketchup
• 2 tsp. relish
• 1 lb. lean ground beef
• Vegetable oil
• 12 slider buns, split
• 1 white onion, minced (1/3 cup)
• Kosher salt, to taste
• Freshly ground black pepper, to taste
• 6 slices Sargento® Creamery Sliced Natural Cheddar Cheese, each slice cut into quarters
• 12 small pieces green leaf lettuce
• 3 small vine-ripened tomatoes, thinly sliced

Instructions

1. 1Mix together the mayonnaise, ketchup, and relish in a small bowl; set the special sauce aside. 
2. 2Roll the beef into 12 small meatballs; set aside.
3. 3Heat a large cast-iron skillet over medium-high heat until very hot, at least 2 minutes. Brush the skillet with oil. Working in three batches, add the buns, cut side down, and cook until golden, 30 seconds to 1 minute. Remove the buns to a plate.
4. 4Brush the hot skillet with more oil and add 4 meatballs, evenly spaced in the skillet. Using the back of a metal spatula, press firmly to smash the meatballs into thin patties. Season with salt and pepper and sprinkle each with some of the onion; smash the onion into the patties with the back of the spatula. Let cook 1½ minutes until golden.
5. 5Flip the patties and cook 1 minute. Arrange two pieces of the quartered cheese over each patty and cover the skillet until the cheese is melted and burgers are cooked through, 1 minute more. Remove the patties to a plate and keep warm. Repeat twice with the remaining meatballs, onion, and cheese. 
6. 6Top the bottom buns with lettuce, tomato, and a smashed burger patty. Spoon about 1 teaspoon special sauce over each patty and sandwich with the top bun.