
Grease your cake pan with butter and line the bottom with parchment paper. Preheat your oven to 180C/350F static.
First, break the white chocolate into small pieces and place in a bowl over a small pot of simmering water. Stir every now and then until completely melted, then remove the bowl and let it cool.
Separate the egg whites and yolks and place them in separate bowls.
Put the butter and 90g (½ cup) sugar in the bowl of a stand mixer and beat them together until light and fluffy using a paddle attachment (you can use a regular electric whisk instead).
Add the egg yolks one at a time until fully incorporated, then add the ground almonds and give it a quick stir. Add the lemon zest, a pinch of salt and the cooled melted white chocolate. Mix everything into the batter until fully combined, then set aside.
Place the egg whites in a large bowl and add 1 tablespoon of fresh lemon juice. Use electric beaters and whisk the eggs until frothy. Add 1 tablespoon of white sugar, then whip the eggs to stiff peaks.
Tip: You should be able to tip the bowl upside down when they are ready. If you tip the bowl to the side and the egg whites slide in the bowl, you need to keep beating them.
Fold the egg whites ⅓ at a time into the cake batter until fully incorporated. Pour the batter into your prepared cake pan and place on a baking sheet.
Bake in the oven for 45 minutes until golden brown on top and a skewer inserted in the middle comes out clean.
Let the cake cool, then remove from the cake pan to a wire rack. Dust with powdered sugar before serving. The cake tastes even better the next day.