Fry the 12 strips of bacon in a cold skillet over medium heat for 8 to 10 minutes, flipping once, until crisp. Transfer to a paper-towel-lined plate and leave about 1 tsp of fat in the pan.

Divide the 2 lbs ground beef into 8 equal patties, roughly 4 oz each and 1/2 inch thick. Season both sides with the 1 tsp kosher salt and 1/2 tsp black pepper. Press a small indent in the center of each.

Heat the skillet with reserved bacon fat over high heat, adding the 1 tbsp neutral oil if the pan looks dry. Sear 4 patties for 2 minutes on the first side, flip, top each with 1 slice of American cheese, and cook for another 90 seconds. Repeat with the remaining 4 patties.

Reduce the heat to medium and toast the 4 brioche buns cut-side down in the same pan for 60 to 90 seconds, until golden.

Stir together the 4 tbsp mayonnaise and 4 tbsp ketchup until smooth.

Spread sauce on both sides of each bun, stack 1 patty, 3 bacon strips, a second patty, and 3 more bacon strips, then press on the top bun and serve immediately.