This is a really nice filling sandwiched between tiny meringues for serving with coffee or for piping onto cakes. It should be completely smooth with all grains of sugar completely dissolved. To make chocolate filling add 1-2 tablespoons cocoa with the icing sugar.
- Dissolve icing sugar with very little boiling water, only enough to make it just slide into butter but not be watery.
- Beat butter until soft and creamy, then add icing sugar, a little at a time and beat until white and creamy - taste before all the icing sugar has been added to see if it is sweet enough, only add the rest if it is needed.
- Add 1 tbs of boiling water, beat again, then add 1 tbs cold water.
- Continue beating until smooth, keep adding alternately a little boiling water then cold water until sugary taste has gone.