1. Heat your oven to 180°C/Gas 4. Grease the base and sides of two 20cm loose-based cake tins and line the bases with baking parchment.
2. Sift all the flours together with the baking powder and xanthum gum into a bowl.
3. In another large bowl, beat the butter and sugar together until light and fluffy. Add the eggs, one at a time, beating well after each addition and scraping down the sides of the bowl with a spatula. Add the flour mixture and fold in, using the spatula or a large metal spoon until just fully incorporated.
4. Divide the mixture between the prepared cake tins and gently smooth the surface with a palette knife to level.
5. Bake in the centre of the oven for 25-30 minutes, or until the sponges are risen, golden and slightly shrunk from the sides of the tins. Leave in the tins for a few minutes, then remove and place on a wire rack to cool completely.
6. Choose the best-looking sponge for the top layer and then lay the other one, top side down, on your serving dish. Spread the jam over this bottom layer.
7. Whip the cream in a bowl to soft peaks and spread on top of the jam then place the other cake layer on top. Dust with sifted icing sugar or caster sugar to finish.