1 large white onion
340 g ground beef round
1 teaspoon Kosher salt
1/2 teaspoon freshly ground black pepper
4 slices American cheese, cut into thirds
60 ml mayonnaise
1 tablespoon ketchup
1 teaspoon mustard
1 tablespoon sweet pickle relish
Step 1
Slice the center portion of the onion into 4 half-inch thick slices, and set aside the smaller ends for another use. Divide the beef into 4 portions and shape each into a very thin patty. Season the patties with salt and pepper.
Step 2
Heat a large skillet over medium-high heat. Working in batches, add 2 onion slices to the pan and cook undisturbed for about 2 minutes. Add 2 patties and continue to cook until golden brown, about 2 to 3 minutes. Flip the onion and burger patties, and cook until golden brown, pressing the burger as it cooks.
Step 3
Place 2 cheese slices on top of one onion slice and both burger patties. Put one burger on the cheese-topped onion slice and top it with the second burger patty. Cover with the remaining onion slice and press down. Flip the burger and cook for 1 to 2 more minutes. Remove from the pan and set aside. Repeat with the remaining onions, burger patties, and cheese.
Step 4
In a small bowl, combine the mayo, ketchup, mustard, and pickle relish. Stir well and serve with the burgers.