1. Heat your oven to 180°C. Line the base of two 20cm cake tins with baking parchment and lightly butter the sides.
2. Put the flour, baking powder, salt, sugar, butter and eggs into an electric mixer or large bowl. Mix on a low speed, or whisk slowly using an electric hand-held whisk, until all the ingredients are evenly combined; do not overmix as this will tighten the mixture and result in a rubbery texture.
3. Split the mixture between the cake tins and put in the oven to bake for 25-30 minutes. The sponge is ready when the top is golden and slightly shrunk from the sides of the tin. Leave to cool in the tins for a few minutes before moving to a wire rack to cool.
4. Select 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 the bottom layer, and then whip the cream to soft peaks and spread over the jam. Place the other layer on top and dust with icing or caster sugar when serving.