Warm a 10” skillet over medium high heat. Meanwhile, slice onion. Add butter and onion to skillet. Sprinkle with sugar. Stir to combine. Stir occasionally until onions start to brown, about 6 minutes.
Preheat grill to high.
While onions are cooking, combine beef, garlic, paprika, cumin, steak seasoning, Worcestershire sauce and 4 ounces of beer in a large mixing bowl. Mix to combine. Portion beef mixture and form into patties slightly larger than your bun. Make a slight indentation in the center of the burger on one side to prevent it from doming up in the center. The indentation will rise as your burger cooks. Set aside.
Pour remaining beer into skillet with onions. Stir to combine, cover and cook for 15 minutes, or until beer evaporates.
Brush burgers with olive oil and lightly sprinkle them with salt.
Place burgers on grill with the indentation side facing up. Close lid and cook for 3 minutes. Flip, brush with barbecue sauce and grill for 3 minutes on the other side. Toast buns on grill.
Assemble burger. Spread 1 tablespoon mayo on each bottom bun. Add lettuce, burger, cheese, caramelized onion and remaining barbecue sauce.
Serve and enjoy!