Mix corn starch and sugar in a 2 cup microwave safe cup or bowl. Microwave on high for 2-3 minutes until the mixture clears and thickens. Stir often and watch carefully as it boils over easily.
Add a small amount of the hot mixture to the beaten egg and mix thoroughly. Return the egg mixture to the remaining hot mixture and stir completely. Microwave of high for 1 minute, stirring at least twice.
Add butter (or margarine) and lemon juice and mix completely. Serve warm or cold with fruit chunks.
We like Melons, Strawberries, Bananas, and Peaches but I'm sure there are a lot of other things that will work just as well.