Mustard flour (also known as mustard powder) is finely ground mustard seeds used as a pungent spice, thickener, and natural emulsifier in cooking. Core Culinary UsesEmulsifying sauces: Binds oil and vinegar together. Making condiments: Base for homemade table mustard.Flavoring meats: Key ingredient in dry rubs.Enhancing sides: Adds punch to mac and cheese