Place all ingredients except the icing sugar in a saucepan and bring to a boil, stirring to dissolve the sugar. Boil for 1 minute. Remove from the heat and let stand for 10 minutes. Beat with an electric mixer, gradually adding the icing sugar. Add the
vanilla. Beat until the mixture thickens but remains thin enough to pour over the cake, 6 to 8 minutes. Pour over the cake immediately, letting the glaze run down the sides. Decorate with nuts.