Use a long, serrated knife to level the top of the large cake, if necessary. Put the cake on a serving plate and cover with two-thirds of the Buttercream, ensuring you spread the mixture evenly over the entire cake. Tint half the Buttercream with your choice of food colouring pastes and use to cover the tops of the cupcakes (you won’t need all the cupcakes, and any leftovers can be frozen for future recipes). Use piping bags with star-shaped nozzles to pipe flower patterns onto the cakes. Divide the Glacé Icing between four small bowls and tint each one with a different colouring paste.