1/3 c. cider vinegar, fill cup with water to make 1 cup
1 tsp. salt
2 tsp. sugar
1/4 tsp. dry mustard
2 tsp. flour, rounded
1 egg
1 tbsp. butter

Combine ingredients, blend until smooth, cook until boiling for 2 or 3 minutes, cool slightly, add 1 tablespoon butter. This dressing is especially good on potato salad - combine with mayonnaise.