Note: These recipes use NZ measurements. 1 c = 1 cup = 250 ml. 1 T = 1 tablespoon = 15 ml. 1 D = 2 teaspoons. 1 t = 1 teaspoon = 5ml. If you're in America, you may find you need a little extra baking powder in recipes that use it.
1/4 c sugar
1 T flour
1 t mustard
1 c water, from corned beef
1/4 c vinegar
Beat egg and sugar, add flour, mustard, then stir in liquid gradually. Microwave on high until thick.
Source: Edmonds Cook Book, page 151