1 c. sugar
2 tbsp. flour
2 tbsp. dry mustard
1/2 tsp. salt
1 egg yolk
1 c. thin cream (or condensed milk)
1/2 c. cider vinegar
2 tbsp. butter

Mix dry ingredients, stir in cream a little at a time. Blend

Beat egg yolk and 3 tablespoons sugar and add to mixture. Cook in a double boiler until thick - add vinegar and cook a little more. Remove from stove and add butter.