First put the flour, cocoa, sugar and a pinch of salt in a bowl. Add the vegan butter in small pieces and crush with your fingers while quickly kneading everything into a smooth dough. Add some cold water if needed.
Form the smooth dough into a flat ball and let it rest in the fridge for about an hour.
Meanwhile, grease and flour the springform pan. Put aside.
Next, prepare the filling by melting the vegan butter and mixing in the remaining ingredients. To do this, mix the skyr, as well as the sugar and starch, together with the vanilla extract or vanilla sugar and lemon juice with the mixer. There shouldn't be any lumps.
After the cooling time, set aside about 220g of the dough.
Preheat the oven to 180° top and bottom heat.
The base is made from the remaining dough.
Roll it out thinly on a floured work surface and line the mold with it. At the end you should have a border about 3 cm high.
Put the filling on the base and smooth it out.
Tear the set aside dough into chunks and spread over the filling in a pretty speckled pattern.
Place the cake in the oven and bake for about 60 minutes.