Betty's Chocolate Fudge Icing

This icing goes very well with Amy's Crazy Cake. Kind of like a marriage made in Heaven. Here's the recipe:

INGREDIENTS
100 g butter, at room temperature
6 tbsp milk
170 g icing sugar (aka confectioner's or powdered sugar) sifted with
30 g cocoa powder

DIRECTION
1. Put the butter and milk in a saucepan and stir over moderate heat. Let it simmer for about 3 minutes. Pour into the sifted icing sugar and cocoa mixture. Mix well until mixture is smooth and glossy.
2. Immediately pour over your cooled cake. Spread icing over the sides and let it run down the sides. Leave to set for about 30 to 50 minutes.