These sliders are great to up your burger-night game.
For the burger sauce: In medium bowl, whisk together all burger sauce ingredients.
For the sliders: Separate bun bottoms from bun tops. Place bun bottoms on serving platter. Use 1-teaspoon measuring spoon to spread 1 heaping teaspoon burger sauce onto each bun bottom. Set aside bun bottoms.
Stack slices of cheese on cutting board. Use chef’s knife to cut into quarters (you will have 24 pieces). Separate cheese into 12 stacks with 2 pieces in each stack. Set aside with bun tops.
Use scissors to cut open seams along sides of quart-size zipper-lock plastic bag, but leave bottom seam intact.
Divide beef into 12 equal portions (2 ounces each) and place on rimmed baking sheet. Use your hands to roll each portion into ball. Wash your hands.
Heat 1 teaspoon oil in 12-inch nonstick skillet over medium-high heat until just beginning to smoke, about 3 minutes. (You should start to see wisps of smoke coming up from oil; you may need to get eye level with skillet to see this. Turn on your stove’s vent hood, if you have one.)
Use spatula to transfer 6 patties to skillet. Sprinkle patties evenly with ¼ cup chopped onion. Use back of spatula to press onion firmly into patties. Cook patties, without moving them, for 2 minutes.
Reduce heat to medium. Use clean spatula to carefully flip patties. Top each patty with 2 slices of cheese and 1 bun top.
Carefully pour 2 tablespoons water into empty spot in skillet (do not wet buns) and cover skillet with lid. Cook, covered, until burgers are cooked through and cheese is melted, about 2 minutes. Turn off heat.
Use oven mitts to remove lid. Transfer burgers to bun bottoms. Cover burgers with large piece of aluminum foil to keep warm.
Use spatula to carefully scrape browned bits out of skillet and discard (skillet will be hot!). Repeat steps 7 through 11 to cook second batch of sliders with remaining 1 teaspoon oil, 6 patties, ¼ cup onion, American cheese, bun tops, and 2 tablespoons water. Serve immediately.
These cheesy, onion-studded sliders are inspired by the ones made famous by White Castle, which has been slinging mini burgers since 1921. To give our sliders their iconic gooey cheese and pillowy buns, we enlisted the power of steam. Adding a splash of water and putting a lid on the skillet traps the hot steam, quickly melting the cheese and gently softening the bun tops. (Just make sure not to splash the bread!) And if you really want to replicate the fast food experience at home, serve these sliders with french fries.