Ingredients
4 eggs
1 cup sugar
1 teaspoon all-purpose flour
3/4 cup vinegar (white or apple cider)
1/4 cup water
butter (about the size of one egg)
1/8 teaspoon dry mustard
Method
Lightly beat the eggs in a bowl. Stir in the sugar and flour, then add the vinegar and water. Cut the butter into small pieces and add it to the mixture along with the dry mustard. Transfer the mixture to a double boiler and cook over gently simmering water, stirring frequently, until the mixture thickens to a custard-like consistency. Remove from heat and let cool slightly before using. Store any leftovers refrigerated.