1/3 to 1/2 c. dry mustard
1/2 c. white vinegar
1/2 c. sugar
1 egg yolk

Combine mustard and vinegar in a small bowl. Blend well. Cover and let stand at room temperature, 8 hours. Combine mustard mixture, sugar, egg yolk in a small saucepan. Cook over low heat until slightly thickened, stirring occasionally. Cover and store in refrigerator. Serve at room temperature. Yield: 3/4 cup.