In the UK we make butter cream this way
250 grams of butter
500 grams icing sugar
butter at room temp – into a mixer beat for 5 mins then add icing sugar on slow until all mixed together plus a couple of tablespoons of milk
1 teaspoon of vanilla extract
then you can add what ever flavours you wish – lemon – coffee – orange – chocolate etc just omit the vanilla
beat for about 5 mins
hope this helps
