Reduce heat and gradually add cheese; stirring until melted. Continue to cook and stir until mixture is reduced by 1/3.
Remove from heat. Add mustard; stir until blended. Pour into storage container. Refrigerate until ready to serve as a condiment to grilled brats.
Notes
Grilling suggestion: Blend 1 cup Gorgonzola mustard with 1/3 cup dark beer. Use as brushing or basting sauce for brat kabobs, whole brats or vegetables when grilling.