Cheeseburger Sliders with Onions

Steps

1. Place a griddle or large 12-inch cast-iron skillet on the grill and set to medium-high. Season beef with salt and pepper and shape into 12 balls. With a mandoline or slicer, shave onion into paper-thin slices. Fold each slice of American cheese into quarters to make 4 squares for a total of 24 squares.
2. Add 4–6 sliders to the griddle or skillet (do not overcrowd skillet) and top each with a handful of sliced onions. With a stiff metal spatula, firmly press onions into beef to flatten. Cook until burgers are nearly cooked through and onions are starting to steam, 4–5 minutes.
3. Flip burgers with spatula. Place 2 cheese squares on each slider. Cover and cook until cheese is melted, 1 minute. If onions begin to cook too quickly, reduce heat to low.
4. Place bottom halves of 6 slider buns onto burgers, cut-sides down. Scrape the sliders off the griddle or skillet and place right-sides up on a platter. Top with half of pickle chips and ketchup. Add tops of buns. Repeat cooking and assembly with remaining beef, onion, cheese, slider buns, pickle chips and ketchup.