1 (2 oz.) can mustard powder
3/4 c. white sugar
3/4 c. white vinegar
4 eggs, beaten
4 tbsp. butter

Combine first four ingredients in a double boiler (or in a microwave-safe bowl) and cook until thickened slightly. (Stir to keep from burning or lumping.) Remove from heat and blend in butter. Stir until smooth. Cool. Store in refrigerator in a tightly sealed jar.