Place the ground brisket and ground short ribs into a large bowl.

Season with the Worcestershire sauce, soy sauce, onion powder, and garlic powder.

Use your hands to gently mix everything together, being careful not to overwork the meat.

Form the mixture into 6 equal-sized patties.

Place each patty onto a platter or baking sheet lined with parchment paper.

Place the mayonnaise, relish, chili sauce, grated onion, white wine vinegar, and sugar into a small bowl.

Stir the ingredients together until completely smooth.

Season the sauce with 1 teaspoon of kosher salt and 1 teaspoon of coarse black pepper.

Heat an outdoor grill, indoor grill pan, griddle, or cast-iron skillet to high heat.

Right before grilling, generously season both sides of the patties with salt and pepper. (Salting right before cooking ensures a juicy burger).

When the grill or pan is smoking hot, place the burgers onto the heat.

Do not move the burgers until they are ready to release from the heat, about 4 to 5 minutes.

Slide your spatula under the burger; if it sticks, give it a bit longer.

Flip the burgers and cook on the second side for another 3 to 4 minutes.

Cook to an internal temperature of 145°F for medium-rare, or test doneness by pressing the center to see if it bounces back.

Transfer the burgers to a platter, top with cheese, and let them rest while the cheese melts.

Reduce the grill heat to medium-low.

Brush the inside of each brioche bun with the softened butter.

Place the buns, butter-side-down, onto the grill and toast until just golden.

Place the rested burgers onto the bottom buns.

Generously slather the patties with the house-made burger sauce.

Crown the burger with the top bun and serve immediately with your favorite extra toppings.