1. Add the flour, sugar, and salt to a large bowl. Add the cold butter in small pieces to the bowl and cut into pea-sized pieces with a pastry blender*. Add the water and mix everything until the dough starts sticking together. It’s fine to see some dry spots here and there but you should be able to form a ball that holds its shape. Wrap in plastic wrap and place in the fridge for about 30-40 minutes.

2. While the dough is resting, boil the potatoes in plenty of salted water. Drain, rinse with cold water, then peel and mash with a potato masher. Set aside and allow to cool.

3. Preheat the oven to 390°F (200°C). Line a 9.5 inches (24cm) springform tin with some baking parchment and grease lightly. Roll out the dough on a lightly floured surface slightly larger than the springform tin, transfer to the tin and press down on the bottom and sides. The edge should be at least 1.6 inches (4cm) tall. Prick the bottom several times with a fork, place a piece of baking parchment on the dough and fill up with some baking beans* or similar. Blind bake the base for about 20 minutes, then remove the baking beans and baking parchment and bake the base for another 5 minutes – the bottom should show some color. Remove from oven and let cool a bit. Do not turn off the oven.

4. For the filling, mix the low-fat quark with the cream cheese and sugar in a large bowl. Add the egg yolks and mix until well combined. Add the ground hazelnuts and mashed (cooled) potatoes and stir in. Lastly, add the raspberries and blueberries and fold in carefully so you don’t crush them. Transfer to the pre-baked cake base and smooth out the top. Return to the oven and bake for about 25 minutes.

5. While the cake is in the oven, prepare the meringue topping. Whisk the cold egg whites in a tall container with a hand mixer until they start looking foamy. While still whisking gradually add the sugar. Continue whisking until you got a very thick and glossy meringue – takes about 2-3 minutes.

6. Remove the cake from the oven after 25 minutes of baking time and spread the meringue on top of the cake. You can pile the meringue up a bit or create a smooth layer – whatever you think looks best. Return the cake to the oven and bake for another 8-10 minutes. Remove the finished cake from the oven and let it cool completely in the tin.