| 1 1/2 lb • ground beef | 
| 2 tsp • Worcestershire sauce | 
| 1 teaspoon • kosher salt | 
| 1/2 teaspoon • ground black pepper | 
| 12 slice • sourdough bread | 
| 1/2 cup • secret sauces | 
| 3 • medium vidalia onions, thinly sliced | 
| 6 slice • Cheddar cheese | 
| 8 tbs • unsalted butter | 
| secret sauce: | 
| 1/4 cup • dijon mustard | 
| 1/4 cup • mayonnaise | 
| 1 tablespoon • barbecue sauce | 
| 1/2 teaspoon • hot sauces | 
| •in a small bowl, stir together mustard, mayonnaise, barbecue sauce, and hot sauce. store, covered, in refrigerator up to 3 days. | 
1.In a large bowl, combine ground beef, Worcestershire, salt, and pepper. Shape ground beef into 6 oval patties. 
2.In a medium cast-iron skillet, melt 2 tablespoons butter over medium heat. Add onion. Cook, stirring occasionally, until onion is soft and golden brown, approximately 35 minutes. 
3.In a large cast-iron skillet, cook patties over medium-high heat until browned and cooked through, approximately 2 minutes per side. Remove skillet from heat. Remove patties from skillet; wipe out skillet. 
4.Layer 1 bread slice with 1 tablespoon Secret Sauce, 2 to 3 tablespoons caramelized onions, 1 slice cheese, 1 patty, and another 1 tablespoon Secret Sauce. Top with another bread slice. Repeat with remaining bread, Secret Sauce, caramelized onions, cheese, and patties. 
5.Heat skillet over medium-high heat. Melt 2 tablespoons butter in skillet. Working in batches, cook sandwiches, flipping once, until golden brown and heated through, approximately 3 minutes per side. Add remaining butter to skillet as needed. 
 
 Source: cookingfamily.feednews.xyz
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