BBQ sause/ marinade

BBQ/Fondue, Ingrediënten: 1 stick butter 1 small or 1/2 medium onion, very finely minced 1-2 cloves garlic 3/4 cup brown sugar, packed into the measuring cup firmly salt/pepper several shakes of hot sauce 1 teaspoon yellow mustard hot red pepper flakes 1 1/2 cups ketchup (up to 2 cups) 2 Tablespoons red wine vinegar