Cook the bacon in a skillet over medium heat for about 5-7 minutes until crispy. Drain most grease, leaving about a tablespoon.

Add sliced onions to the skillet, reduce heat to medium-low, and cook for 10-15 minutes until golden brown. Add Irish stout and let it reduce by half while scrapping the bottom of the skillet.

In a mixing bowl, combine ground beef with Worcestershire sauce, salt, and pepper. Form into four patties slightly larger than the buns.

Heat a grill or skillet over medium-high heat. Cook patties for 3-4 minutes on one side, then flip, adding cheddar cheese during the last minute to melt.

Mix sour cream and Dijon mustard together in a bowl until smooth for the sauce.

Toast the brioche buns cut-side down in a skillet with melted butter for 2-3 minutes until golden brown.

Assemble by placing a patty on the bottom half of each bun, topping with caramelized onions, crispy bacon, and creamy sauce. Cap with the top half of the bun.

Serve hot with sides like sweet potato fries or salad.