Combine sugar, cream and butter in a small saucepan and bring to a boil. Remove from head and mix in vanilla and amaretto liqueur.
If you like your cake particularly boozy, pour an extra 1/4 cup of amaretto liqueur over hot cake and let it absorb for a few minutes prior to pouring the icing over.
Pour icing over hot cake - makes a lot of icing but use all of it!
Serve warm with whipped cream or vanilla ice cream. Keep refrigerated for several days.