Heat a large skillet over high heat. Add safflower oil, and swirl to coat. Reduce heat to medium. Cook Vidalia onions, stirring often, until very soft, about 30 minutes. Stir in mustard powder, salt, and turmeric. Cook, stirring often, for 3 minutes. Stir in cider vinegar, and raise heat to high. Add pale ale, and cook, stirring often, until mixture is thick, about 5 minutes. Let cool completely.
Storage: Mustard can be refrigerated for up to 1 week.