Melt butter in large skillet on medium heat. Add onions, 1 teaspoon of the Marinade Mix and chipotle chili pepper; cook and stir 7 to 8 minutes or until onions are golden brown. Add 2 tablespoons of the beer and sugar; cook and stir 1 to 2 minutes or until beer has evaporated. Set aside.
Mix remaining Marinade Mix, remaining 1/3 cup beer and Worcestershire sauce in large bowl until well blended. Add ground beef; mix lightly. Shape into 6 patties.
Grill over medium heat 4 to 6 minutes per side or until burgers are cooked through (internal temperature of 160 F). Add cheese slices to burgers 1 minute before cooking is completed. Toast rolls on the grill, open-side down, about 30 seconds or until golden. Serve burgers on toasted rolls with caramelized onions. Garnish with desired toppings and condiments.