Flavour (original recipe used 1 tablespoon instant coffee, can substitute 1 teaspoon vanilla essence etc.)
Mix 1/3 cup milk with cornstarch in bowl. Boil rest of milk with sugar in saucepan. If the flavour is something that needs dissolving (eg the instant coffee), stir it into the milk. Stir milk mixture into corn starch mixture. Return to saucepan and boil mixture while stirring until thick and smooth.
Take off heat and allow to cool, stirring often. Add flavour if not already added. Beat butter in large bowl until smooth. Add milk-cornstarch mixture and beat well. Makes enough to fill and top a 9 inch cake.