1. Preheat the oven to 350°F (180°C). Line a 9 inches (23cm) springform tin with baking parchment grease lightly. Set aside. Melt the butter and let cool down again.

 

2. Divide the eggs and add the egg yolks and xylitol (or sugar) to a large bowl. Mix on high speed until light and fluffy. Add the melted and cooled butter and mix until well combined. Mix the flour with baking powder and lemon zest and then add to the bowl. Gradually add the lemon juice and mix all until just combined. Whisk the egg whites with a pinch of salt in a separate bowl until stiff peaks form. Add in two batches and carefully fold in – you want to keep as much volume as possible. Pour the batter into the prepared baking tin, smooth out the top and bake for 16-20 minutes until lightly golden. Insert a toothpick into the center of the cake to see if it is done. Turn off the oven, open the door a bit and leave the cake in the oven for another 30 minutes to cool down slowly. Then take out of the oven and let cool down completely on a wire rack. Dust with some confectioners’ sugar before serving and decorate with kumquat or lemon slices.