INGREDIENTS
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1½ pounds ground beef
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2 teaspoons Worcestershire sauce
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1 teaspoon kosher salt
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½ teaspoon ground black pepper
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12 slices sourdough bread
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½ cup Secret Sauce (recipe follows)
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1 cup Caramelized Onions (recipe follows)
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6 slices Cheddar cheese
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6 tablespoons unsalted butter