1. Separate the eggs. Put the whites in a dry bowl, add two-thirds of the 120 g sugar and whisk on high speed until stiff.

2. Put the yolks in another dry bowl with the remaining cake sugar and beat for 1 minute. Add the yogurt and beat well.

3. Mix the flour with the baking powder and add to the yolks. Mix on low speed, then stir in the coarsely ground walnuts. Gently fold in the egg whites with a spatula.

4. Pour into a 20 × 15 cm baking tin. Bake on a low shelf in a preheated oven at 180°C for 30 minutes. Turn off the oven and leave the cake inside for another 20 minutes.

5. While the cake bakes, boil the 200 ml water and 150 g sugar for 1 minute. Add the vanilla sugar, remove from the heat and leave to cool. Pour the cooled syrup over the warm cake.

6. Leave for several hours before cutting and serving.