1. For the dough add the flour and confectioners‘ sugar to a mixing bowl and combine. Add the butter in small pieces and the egg yolk – both should come straight from the fridge, so they are really cold. Add the salt and some lemon zest and mix/knead everything to get a nice and smooth dough (e.g. with a handheld mixer with dough hooks). Shape the dough into a ball, flatten it, then wrap it in plastic wrap. Place it in the fridge for at least 30 minutes.

2. Line a springform tin (18cm)* with baking parchment and grease it lightly. Roll out 2/3 of the dough into a circle as big as the springform tin and place it inside the baking tin. Use the rest of the dough and shape it into a long log. Press that log to the sides of the springform tin to create a crust for the cheesecake filling – the edges should be at least 5cm tall. Place in the fridge until needed.

3. Preheat the oven to 180°C (350°F). Mix the cornstarch with the milk until completely dissolved. Set aside. Add the heavy cream and sugar to a small saucepan and bring to a boil while stirring constantly. Add the cornstarch mixture and let the custard cook for a moment while stirring constantly until it has nicely thickened. Remove from the heat and let cool down a bit.

4. Mix the quark, egg yolks, vanilla extract, lemon juice, lemon zest and salt in a small bowl until well combined. Add this mixture to the saucepan and mix it into the still warm custard. Transfer the cheesecake filling to the prepared springform tin and smooth out the top. Bake the cheesecake for about 15 minutes, then reduce the temperature of the oven to 150°C (300°F) and bake the cake for another 15 minutes. Take the cheesecake out of the oven and let cool down completely on a wire rack. Place the cooled cake in the fridge for at least 5-6 hours or overnight.

5. Take the cake out of the fridge about 30 minutes before serving. Wash the blueberries and let them drain, then combine them with the blueberry jam and spoon the mixture on top of the cheesecake.