Ingredients

1 lb. ground beef (80/20)
8 slices of cheese (I used American)
2 tbsp butter
4 burger buns
1 tomato, sliced
1/2 onion, sliced
dill pickles
1/3 head iceberg lettuce, thinly sliced

Mustard sauce:
1/2 cup mayo
2 tbsp whole-grain mustard
1 clove garlic, grated
1 tbsp, hot sauce (I used Cholula)
1 tbsp ketchup
kosher salt and pepper to taste

Instructions

Prepare the mustard sauce. In small bowl, mix together all of the ingredients. Refrigerate until ready to use.
Portion the ground beef into 4 even balls (4 oz each). Heat a large, dry cast-iron skillet over medium-high heat. Once the pan is hot, place the balls in the skillet spaced out as much as possible. You might have to do two at a time. Smash them with a spatula or burger press to about 1/2 inch thick. Season generously with salt and pepper. Let them sear for about 3 minutes and then flip. Season again with salt and pepper and cook for another 3 minutes. Add two slices of cheese to each patty and a splash of water. Cover with lid or foil and steam until the cheese melts. Remove from the heat. Toast buns and season tomatoes with salt. To plate, spread mustard sauce on the bottom bun, top with tomato, pickles, lettuce and beef patty. Top with more sauce and the top bun.