Combine all ingredients in a nonreactive saucepan. Simmer until onions are tender and translucent.
COOKS NOTES: Butter! No substititute. Broth is an important ingredient to the mop. For brisket he uses beef broth, for chicken he uses chicken stock he makes himself from the backs and tails he cuts away when preparing chicken. He also incorporates the spices from the rub to maintain the same balances of flavors.
Ingredients
1 can beer , flat
1 cup beef stock
1/2 cup cider vinegar
1/2 cup onion , chopped
1/2 stick butter
2 tablespoons worcestershire sauce
2 tablespoons good quality hot sauce
2 tablespoons dry rub