Bring the butter to room temperature. Sift the icing sugar into a mixing bowl.
Zest the orange. Split the vanilla pod in half and scrape the seeds into icing sugar. Beat the icing sugar, vanilla and butter until creamy. Stir the Grand Marnier and the zest through the butter cream.
Place in a piping bag ready to pipe.
«Try using other types of citrus fruit for a different flavoured buttercream. »