1. Preheat the oven to 140°C (275°F/Gas 1). Grease a 25cm (10in) springform cake tin with the butter and line the base with baking parchment, making sure the paper is exactly the same size as the base.
2. Cream the butter and sugar in a large bowl. Add an egg yolk, mix well, then add a little of the ground almonds and combine well. Repeat until all the yolks and almonds have been added to the mix. Add the vanilla extract and combine well.
3. In a clean separate large bowl, beat the egg whites to stiff peaks with an electric hand whisk. Gently fold the egg whites into the cake mix with a metal spoon to keep the mix as fluffy and light as possible. Keep 6–12 raspberries aside to use as decoration later. Transfer half the mix to the prepared cake tin, arrange half the raspberries on top, then add the rest of the cake mix and finish with the rest of the raspberries. Don’t combine the raspberries with the cake mix, as they will break up and discolour the cake.
4. Bake in the oven for 45 minutes–1 hour until cooked through. To test if the cake is cooked, insert a clean skewer into the centre of the cake. If the skewer is clean when you take it out, remove the cake from the oven. If not, cook for a little longer and test again.
5. Place the cake on a wire rack and allow to cool. Once cool, carefully remove the springform tin and baking parchment. Decorate the top of the cake with the reserved raspberries and serve.
Neal's Yard Remedies Healing Foods, published by DK, £16.99, dk.com.