Thick and Hearty BBQ Sauce

3/4 cup cider vinegar
1/2 cup ketchup
1/4 cup chili sauce
1/4 cup Worcestershire sauce
1/4 cup finely chopped onions
2 large garlic cloves, finely minced
1 Tbsp dark brown sugar
1 Tbsp fresh lemon juice
1/2 tsp. dry mustard
1/4 tsp red pepper flakes (optional)

Combine all in a saucepan, bring to a boil over medium heat stirring occasionally. Reduce heat and simmer uncovered 40 minutes. Stir occasionally.