Heat milk in a double boiler. While getting hot, go ahead and beat your eggs and sugar together in a large bowl. When milk is fairly hot, add some to your egg/sugar mixture while beating.This keeps your eggs from curdling. Pour mixture into pan of milk and cook [stirring] until it coats a wooden spoon. Remove from heat and when fairly cool, add the vanilla. Pour into an empty milk jug and refrigerate.
I usually double this receipe. Since I don't have a large double boiler, I use an iron skillet with about 1 inch of water in the bottom and set my large pan in it. Works great.