Ingredients

For the ShackSauce

½ cup  mayonnaise

1 tablespoon Dijon mustard

1 teaspoon ketchup

¼ teaspoon  dill pickle brine

Pinch cayenne pepper

For the ShackBurgers

4 hamburger potato buns

4 tablespoons unsalted butter, melted

ShackSauce

4 pieces green-leaf lettuce

Eight ¼-inch slices plum tomatoes

1 pound cold ground beef, formed into four 1-inch-thick circle

salt and freshly ground pepper, to taste

Onion powder, garlic powder and chilli flakes

4 slices cheese

Directions

Make the ShackSauce: In a small bowl, stir all of the sauce ingredients until smooth, then set aside.

Make the ShackBurgers: Heat a large cast-iron skillet over medium-low heat. Meanwhile, open the hamburger buns and brush both sides liberally with the melted butter. Working in 2 batches, place the buns onto the heated skillet, buttered-sides down, and cook until golden brown, 2 to 3 minutes. Transfer to a plate and spoon 1 tablespoon of sauce on each top bun, along with a piece of lettuce and 2 slices of tomato.

Increase the heat to medium and let the pan heat up for 2 to 3 minutes. On a plate, season both sides of each puck of ground beef with salt and pepper.

Place the pucks into the cast-iron skillet, leaving plenty of room between them. Using a large, sturdy metal spatula, firmly smash each puck into a ⅓-inch-thick round patty. Cook the burgers without touching them until the edges are brown and crisp, 2½ minutes, then flip them. Place a slice of American cheese on each burger and continue to cook until medium, 1 minute more.

Transfer a cheeseburger to each bottom bun, then sandwich with the top bun and lettuce and tomato, and serve.