Ingredients

• 2 1/4 pounds 90% lean ground beef (such as sirloin)
• 1 large onion, roughly chopped
• Kosher salt and freshly ground pepper
• 36 slider buns, split
• Dill pickle slices, ketchup and mustard, for topping

Instructions

1. Form the meat into 36 golf ball-size balls. Pulse the onion in a food processor until finely chopped.
2. Heat a cast-iron skillet over high heat. Working in batches, add the meatballs to the skillet and smash them very flat with a spatula. Season with salt and pepper, then sprinkle the onion over the patties. Cook 1 minute, then flip and smash the burgers with the spatula again. Cook 1 more minute for well done; place both halves of the buns on top of the patties to steam for the last few seconds of cooking.
3. Serve the burgers on the buns; top with pickles, ketchup and mustard.
4. Photograph by Tina Rupp