Put the butter and cream cheese in a mixing bowl (see tips) and beat with an electric mixer until combined and smooth.
Sift in the icing sugar in batches, beating well between each addition until smooth.
The butter and cream cheese for the buttercream need to be at the same temperature before they’re mixed. Take them out of the fridge at the same time to warm up. If your buttercream is too soft after mixing, chill until firmer.