Cream together the butter, orange zest and half the icing sugar until light and fluffy (it’s easiest to use a food processor or stand mixer). Beat in the rest of the icing sugar and the brandy.
Pile the butter into a serving dish, swirl the top with a palette knife, then chill until needed. The mixture will be soft at this stage but it will firm up in the fridge. Once firm, cover with cling film. It will keep for 2 weeks in the fridge.