In a small deep saucepan, combine all ingredients over low heat. Stirring until the mixture is smooth and warm (but not hot to the touch), about 3-5 minutes.

Quickly pour over cake, it will slowly self-level but use an offset spatula if it's cooling too quickly to spread the icing to fill in any gaps. Do this quickly as you don't want any spatula marks left in the icing, it must still be warm enough to self-level after you've spread it.

Allow to dry completely at room temperature.