Martha’s Barbecue Sauce

1 tablespoon olive oil $0.07 1 small onion, finely chopped $0.47 4 cloves garlic, minced $0.04 1 tablespoon mustard powder $0.09 1 teaspoon red pepper flakes $0.23 3 tablespoon light brown sugar $0.03 2 cups ketchup $1.22 1/3 cup Worcestershire sauce $0.64 1/3 cup cider vinegar $0.19 1 tablespoon molasses $0.06 1/4 teaspoon ground black [...]