1 1/2 cups apple cider vinegar
1/2 cup ketchup
1/2 cup yellow mustard
2 tablespoons Worcestershire sauce
1 tablespoon Tabasco sauce
1 teaspoon kosher salt
1 teaspoon black pepper
2 tablespoons cold unsalted butter
Reduce the root beer to 1 cup over medium heat in a large saucepan -- this takes about one hour. Add the Apple Cider Vinegar, ketchup, Yellow Mustard, lemon juice, Worcestershire Sauce, Tabasco, salt and pepper. Stir well and simmer for twenty minutes. Finish the sauce by whisking in the cold butter for extra body and flavor.