Sift the icing sugar and caster sugar into a large bowl, then stir in the beaten egg.

Place the bowl over a pan of simmering water and whisk for 10 minutes, until the mixture is thick and fluffy.

Remove the bowl from the heat and sit the base in 5cm of cold water. Whisk in the almond extract and brandy and continue to whisk until the mixture is cool.

Stir in the ground almonds and knead on a surface lightly dusted with icing sugar, forming a firm paste.

Roll out the amount needed on a clean surface dusted with icing sugar. You can now either use this to top your cake or place it in moulds to create marzipan sweets in various festive shapes.