Microwave Confectioner’s Cream
Whisk the half-and-half, cornstarch, and sugar together in a large microwave-safe bowl or a 1-quart glass measuring cup. Put the bowl in a microwave oven set to full power and cook for 1 minute. Stir the mixture and cook for 2 to 3 minutes more, a minute at a time, until the mixture comes to the boil and thickens slightly.
While the liquid is heating, whisk together the yolk and vanilla in a small bowl.
Slowly whisk a little of the hot liquid into the yolk. Pour the yolk mixture into the boiled mixture, whisk well, and return the bowl to the microwave oven. Cook the cream for 30 seconds longer, then remove the bowl from the oven and stir again. The cream’s consistency is like that of lemon curd. Scrape the cream into a small container, press a piece of plastic wrap against the surface of the cream to prevent a skin from forming, and cool to room temperature. Seal the container and chill. The cream can be made up to 3 days ahead and kept refrigerated.