Divide ground beef into 8 equal balls about the size of a ping-pong ball (3-ounces each); refrigerate.

In a small mixing bowl, whisk together mayonnaise, mustard, grated onion, hot sauce and Worcestershire to create a special sauce; refrigerate.

Using either a large cast iron griddle or 2 large cast iron pans heated to high, toast buns with butter; reserve to plates.

Space beef balls on hot cooking surface. Using a large metal spatula, smash each ball to 1/4-inch-thick patties.

Season patties with 1-teaspoon of reserved special sauce per patty; salt and pepper. Sear 2-3 minutes or until some fat begins to bubble up in center of patty. Quickly flip and top 4 of the patties with a slice of cheese.

Sear another minute and place a plain patty atop a cheese patty; remove from cooking surface.

Build burgers with a smear of special sauce on bottom bun followed by shredded lettuce, tomato, double burgers and top bun.