Bake the sponge layers

• Cream the softened butter with the caster sugar until pale and fluffy.
• Beat in the eggs one at a time, then add the vanilla extract.
• Fold in the flour, baking powder and salt, then loosen with the milk.
• Divide between the greased cake pans and bake at 180 °C until a skewer comes out clean.

Make the Swiss meringue buttercream

• Whisk the egg whites with the caster sugar in a bowl over a saucepan of simmering water until the sugar dissolves and the mixture reaches 70 °C.
• Transfer to the stand mixer and whip to a stiff, glossy meringue cooled to room temperature.
• Add the softened butter piece by piece, whipping until smooth and silky.
• Flavour with the vanilla extract and divide into bowls.

Colour the buttercream

• Tint each bowl of buttercream with the pastel pink, purple and blue food colouring.
• Mix until the colours are even.

Fill and crumb coat the cake

• Stack the cooled sponge layers with buttercream between each.
• Cover the whole cake with a thin crumb coat and smooth with the spatula.
• Chill until the buttercream is firm.

Pipe the unicorn mane

• Fill the piping bags with the coloured buttercreams.
• Pipe rosettes and swirls around the top and down the side to form the mane.
• Add the sprinkles over the piped buttercream.

Finish the unicorn

• Shape and place the horn and ears on top of the cake.
• Brush the horn with edible gold leaf.
• Chill the cake until ready to serve.