Allow the melted chocolate to cool for 10 minutes before adding to the whipped butter and sugar. Beat until well combined. If your icing sugar is a bit old and pebbly, sieve the icing sugar to ...
Sift in the icing sugar, then work it into the butter ... or add flavourings such as cocoa or melted chocolate, or lemon or orange zest. Buttercream will keep in the fridge for a few days ...