Divide the ground beef into four equal portions (about 4 oz / 113 g each). Lightly form into thin patties about 4 inches (10 cm) wide and 1/2 inch (1.3 cm) thick. Season the exterior of each patty with a sprinkle of salt, pepper, and a pinch of garlic powder. On two of the patties, evenly place a pile of torn cheese in the center (about 1 slice worth each). Top each cheese-topped patty with one of the remaining patties and press the edges together firmly to seal the cheese inside, creating a sealed pocket. Smooth the sealed edges and gently flatten to create an even patty about 3/4 inch (2 cm) thick; avoid overworking the meat.

Cook the Juicy Lucys

Heat a heavy skillet or cast-iron pan over medium-high heat. Add the oil to the pan and swirl to coat; add the butter once hot. When butter foams and the pan is hot (but not smoking), place the sealed burgers in the pan, leaving room between them. Cook undisturbed for 3-4 minutes until a deep brown crust forms on the underside. Flip carefully and cook another 3-4 minutes, covering the pan for the last minute to help melt the cheese inside. Use an instant-read thermometer if desired; target internal temperature is 160°F (71°C) for a fully cooked burger with melted cheese center. Remove burgers to a plate and tent with foil to rest for 3 minutes.

Buns & Toppings

Prepare vegetables and buns

While the burgers cook, slice the tomato into four 1/4-inch thick slices. Slice the red onion into thin rings and separate. Toast the brioche buns cut-side down in a separate skillet or in the oven under a broiler until lightly golden, about 1-2 minutes; you can butter the cut sides lightly before toasting for extra flavor.

Assemble: Spread mayonnaise on the bottom bun (about 1 tablespoon per bun) and a dot of ketchup and mustard on the top if using. Place a lettuce leaf on the bottom bun, then position the cooked Juicy Lucy patty (seam-side down) on top. Add a tomato slice, a few onion rings, and two pickle slices. Cap with the top bun and serve immediately.

Condiments (optional)

If preparing the condiments ahead, mix mayonnaise, ketchup, and mustard in a small bowl and adjust seasoning to taste. Spread as desired on buns during assembly.