Cook the bacon: In a skillet over medium heat, cook the bacon until crispy. Transfer to a paper towel-lined plate to drain.
Sauté the onions: Remove excess bacon grease from the skillet, leaving just enough to coat the bottom. Add the sliced onions and cook over medium heat until caramelized, about 10–15 minutes. Pour in the Irish stout and simmer until the liquid reduces by half. Season with salt and pepper. Set aside.
Make the patties: In a bowl, combine ground beef with Worcestershire sauce, salt, and pepper. Form into 4 equal patties, shaping them slightly larger than your buns to allow for shrinkage while cooking.
Cook the burgers: Heat a grill or skillet over medium-high heat. Cook the patties for about 3–4 minutes per side, or to desired doneness. During the last minute of cooking, top each with grated cheddar and cover lightly to help it melt.
Prepare the sauce: In a small bowl, whisk together sour cream, Dijon mustard, and a pinch of salt. Set aside.
Toast the buns: Lightly butter the inside of each bun and toast them in a pan until golden brown.
Assemble the burgers: Start with the bottom bun, then add the cheesy patty, a scoop of caramelized onions, two slices of bacon, and a generous spoonful of the sour cream-Dijon sauce. Finish with the top bun.
Serve: Enjoy immediately with a side of fries or chips, and maybe a cold pint for the full pub experience