Preheat oven to 180°C conventional oven (400° Fahrenheit/Gas 6). Grease a 24cm round cake pan by lightly buttering the base and sides with margarine or butter. Line the base with baking paper, then lightly butter over the baking paper. Add a heaped tablespoon of potato flour (or alternatively rice flour), then turn and shake the tin to coat the butter in flour on the base and sides of the cake pan.
Place the white chocolate in a heatproof bowl set over a pan of simmering water (don’t let bowl touch the water). Cook, stirring using a metal spoon, until the chocolate has melted to a smooth consistency. Remove the bowl with melted chocolate from the heat and allow to cool.
Using an electric mixer or hand beater, beat the egg whites with a pinch of salt until stiff peaks form. With the mixer (or hand beater) running, add the egg yolks, one at a time. Add the sugar, one tablespoon at a time, beating well after each addition.
Place the almond meal in a food processor and process briefly. This step is optional but will make the cake extra smooth. Use a wooden spoon to stir the almond meal into the egg and sugar mixture, one tablespoon at a time. Continue to use the wooden spoon to fold in the melted white chocolate until just combined. Stir in the potato flour (or rice flour), lemon zest and juice. Then stir in the extra virgin olive oil, limoncello and Italian baking powder until well combined.
Note: Potato flour (fecola di patate in Italian) is available in Italian food stores and gourmet delicatessens. A good alterative is to use rice flour.
Pour the cake mixture into the prepared cake pan. Bake for 40-45 mins or until a skewer inserted in centre comes out clean. Allow the Torta Caprese to cool in the cake pan for 10 minutes, then transfer to a wire rack to cool completely.
Note: For best results, complete steps 1-5 in this recipe 1 day ahead – it creates a deeper lemon flavour when eaten the following day.
Dust with sifted icing sugar (confectioners’ sugar) on top of the Torta Caprese (Gluten-free lemon and white chocolate cake) before serving – buon appetito.