Sweet Butter Icing

4 egg yolks
½ cup milk
¾ cup powdered sugar
1 teaspoon vanilla
½ pound sweet butter (unsalted)

Beat egg yolks, add sugar and milk.
Cook in top of double boiler until thick like custard.
Cool, and add to butter which has been creamed.
Mixture must be cool before combining and refrigerated after icing cake.

See Nut Cake recipe