Preheat the oven to 180°C (350°F) fan-forced. Butter a round 20 cm (8 inch) cake tin and line the base with baking parchment.

In a food processor blitz the hazelnuts, white chocolate, cornflour, baking powder, salt and 1 tablespoon of caster sugar until roughly ground. Tip into a bowl, mix in the ground almonds and set aside.

Using handheld electric beaters, whisk the egg yolks, lemon zest and remaining sugar until thick and pale. Mix in the lemon juice and ground almond mixture. Pour over the melted butter to help the mixture come together more easily.

Whisk the egg whites until medium stiff peaks form, adding the extra tablespoon of sugar halfway through. Using a clean metal spoon, gently fold the egg whites into the almond mixture, bit by bit.

Pour the batter into the prepared tin and bake for 40 minutes or until a cake tester inserted in the centre comes out clean(ish). If it comes out covered in batter, bake for another 5 minutes and test again. Remove from the oven and leave to cool in the tin for 45–60 minutes before turning out onto a serving plate.

About 15 minutes before you turn out the cake, make the chocolate ganache. Place the chocolate in a large heatproof bowl. In a small saucepan, gently heat the cream and sugar, stirring until the sugar has dissolved. Bring to a simmer, then immediately remove from the heat. You don’t want the cream to boil or it will split the ganache.

Pour the hot cream over the chocolate in the bowl and leave to sit for 2 minutes, then whisk thoroughly until thick and glossy. Let the ganache cool for
10 minutes – it should be a loose but spoonable consistency that won’t run down the side of the cake.

Gradually spoon the ganache into the centre of the cake and smooth it out to the side using a spatula or the back of a spoon. Cut into slices and serve. The cake will keep in an airtight container for up to 3 days.