In a saucepan, cook onions in oil over moderate heat until tender. Stir in garlic, red pepper flakes and chile powder, and cook for one minute.
Add ketchup, beer, vinegar, water, brown sugar, mustard, Worcestershire sauce, salt, black pepper, and Tabasco sauce, stirring to combine.
Partially cover and simmer until slightly thickened, 15 to 20 minutes. Taste and adjust seasoning, if necessary, with Tabasco sauce. Remove sauce from heat and allow to cool completely.
Sauce can be refrigerated for two to three weeks or frozen for up to a month.Yields: 2 cups