For the CARAMEL Icing: In a mixing bowl, combine egg yolks, 1/4 cup of the sugar, 1/2 cup of cream milk and cornstarch together, mixing well to combine. Set aside. Caramelize the remaining 3/4 of sugar over low heat until becomes light golden brown. Gently add the boiling water and bring back to a boil, stirring well until the caramel is well blended in water. Add the remaining full cream milk and heat mixture. Pour a little of the caramel/milk mixture into the egg yolk mixture to temper the eggs, mixing well until smooth. Add this back into the remaining caramel mixture. Stir well until icing becomes thick and spreadable consistency. Remove from the fire and mix the butter and vanilla, stir well.