Make the Sauce: Mix mayonnaise, tomato sauce, American mustard, vinegar, pickled relish, garlic powder, onion powder, and paprika. Set aside.
Shape the Patties: Portion the beef into 80-gram patties. Press flat between baking paper using a plate.
Cook the Patties: Fry patties in a hot pan, pressing them down. Remove the paper, season with salt and pepper, and melt cheese on top.
Prepare the Buns: Shave off the dome and base from another brioche bun—these will be used for the middle layer in two burgers.
Assemble the Burger: Layer sauce, onions, lettuce, beef patty (cheese side down), middle bun, more sauce, lettuce, pickles, and the second patty. Top with the remaining bun.
