Step 1

Prepare a grill for high heat. Place a cast-iron griddle, flat side up, on grate; heat until very hot, at least 20 minutes.

Step 2

Mix together pickles, mayonnaise, ketchup, adobo sauce, and ½ tsp. salt in a medium bowl; set special sauce aside.

Step 3

Divide beef into eight 3-oz. portions (don’t form into patties). Place 4 portions between 2 sheets of parchment paper, spacing 6" apart, and, using a meat mallet or skillet, firmly smash to create thin patties, about 5" across. Transfer to a baking sheet. Repeat with remaining portions and fresh parchment paper.

Step 4

Wrap all the buns together in a large sheet of foil to make a packet (this will keep buns soft and from getting too toasted on the grill). Place packet on grate and grill, turning once, until buns are warmed through, about 1 minute. Spread sauce over cut sides of buns. Place 3–4 pieces of lettuce on bottom buns and top each with some onion and a tomato slice, if using.

Step 5

Drizzle oil over griddle and use paper towels to evenly coat surface. The oil needs to be hot; you should see smoke almost instantly. Season patties lightly with salt. Place 4 on griddle, seasoned side down, and season top sides lightly with salt. Cook, undisturbed, until outer edges are brown and undersides are very crisp, about 2 minutes. Flip and place a slice of cheese on top of each patty. Cook until cheese is melted, about 30 seconds. Transfer patties to buns with toppings, stacking 2 patties on each bun. Repeat with remaining 4 patties, scraping off any cheese stuck to griddle in between batches.