Ingredients:
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– 1½ pounds ground beef
– 2 teaspoons Worcestershire sauce
– 1 teaspoon kosher salt
– ½ teaspoon ground black pepper
– 12 slices sourdough bread
– ½ cup Secret Sauce (recipe below)
– 3 medium Vidalia onions, thinly sliced
– 6 slices Cheddar cheese
– 8 tablespoons unsalted butter
Secret Sauce:
– ¼ cup Dijon mustard