Buttercream or Butter-Icing

Makes enough to sandwich a 15-18 cm cake.
To sandwich and also coat the outside of the cake, double the following quantities.

50g  dairy-free margarine 
100g sieved icing sugar
flavouring like vanilla, almond, orange or lemon essence or extract, optional
colouring, if desired

In a small bowl, cream the fat for a minute or two, the add the icing sugar and cream together again, adding the flavouring and/or colouring if using.