½ cup Hellman's mayonnaise
1 tablespoon Dijon mustard
1 teaspoon Heinz ketchup
¼ teaspoon kosher dill pickle brine
Pinch cayenne pepper
4 hamburger potato buns
4 tablespoons unsalted butter, melted
4 pieces green-leaf lettuce
Eight ¼-inch slices plum tomatoes
1 pound cold ground beef, formed into four 1-inch-thick pucks
Kosher salt and freshly ground pepper, to taste
4 slices American cheese
- 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 skilletover 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 3minutes. On a plate, season both sides of each puck of ground beefwith 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.