First, gently melt the butter in a saucepan over a very low heat. Once melted remove from the heat and set aside.
Place the flour and icing sugar in a large mixing bowl and add the cocoa powder. Make a well in the centre and add the egg yolk and milk. Remember to keep the white you are going to need this later for the filling.
Add the melted butter and mix to form a dough. Remove about one-third of the dough and wrap well. Then wrap the remaining dough and chill for about 1 hour or until firm.
Preheat the oven to 180℃ (160℃ fan)/350°F/gas mark 4.Lightly grease a 33 x 23 cm (13 x 9in) shallow baking dish. Coarsely grate the larger portion of the dough and spread in even layer over the base of the dish. Return to the refrigerator while you make the filling.
To make the filling
Place the quark in a mixing bowl. Sift in the icing sugar. Add the milk, vanilla extract and egg yolks and beat until well combined.
In a separate bowl whisk the egg whites until standing in stiff peaks. Gently fold the egg whites into the quark mixture.
Pour the cheesecake mixture over the chocolate dough in the dish and spread level.
Grate the remaining chocolate and sprinkle in an even layer over the filling. Bake for 45 minutes. Allow to cool before cutting into slices to serve.
Nutrition information is calculated usingan online nutrition database - is approximate and is meant as a guideline only.
Covered in the refrigerator for up to 3 days. Freeze for up to 2 months. Defrost at room temperature.