Slowly whisk the hot half-and-half into the egg yolk mixture. Then return the partially cooked custard to the saucepan. Stir constantly over medium-low heat until mixture begins to thicken slightly and coats the back of a spoon, about 5 minutes (the approximate consistency of unwhipped heavy cream). Pour hot custard into a bowl without straining. Stir in the vanilla. Put a sheet of plastic wrap directly on the surface of the custard to prevent skin from forming. Set custard aside at room temperature to cool. (Can cover with plastic
Makes about 1 1/2 quarts.