I have had this recipe for years. I make it every Christmas and give it to my neighbors as gifts. It is always a big hit. I use a candy thermometer to help judge when milk is scalded and when the custard is done.
Rinse top of double boiler with hot water to keep milk from scorching. Scald whole milk (approx. 180°). Blend eggs and sugar in blender. Slowly add to scalded milk in top of double boiler stirring constantly. Cook until mixture thickens and coats spoon well (appox. 180º). Remove from heat. Add pure vanilla. Let cool a little then strain into containers. The straining is important to make sure there are no lumps in the custard.