Add the A ingredients to a heat-resistant container and use a whisk to mix well (instead of sifting).
Add the milk a little at a time and mix well. Add the egg yolk and mix well.
Microwave at 700 W for about 2 minutes and 30 seconds (non-wrapped). Mix well, add the egg whites, then mix again.
Microwave again at 700 W for 1 minute 30 seconds. As the finishing touch add butter, vanilla extract, rum and brandy and knead well.
Once finished it'll be smooth as shown in the picture.
Make into a 15 x 18 square shape, wrap, and store in the freezer once it's cooled off.
Story Behind this Recipe
This is my custard insert sheet for bread. A light sheet that uses the whole egg. This sheet lets you try various alterations.
The heating time will vary depending on the wattage of your microwave, so please adjust accordingly. If you substitute part of the milk for heavy cream you'll get a rich sheet with a kick. You can omit the liquor if you like.