Mix the ingredients for the cake dough into a shortcrust pastry and chill for at least 30 minutes.
Meanwhile, prepare the filling. Sort the blueberries, wash and drain well.
In a bowl, mix sour cream, sugar, cornstarch, eggs and lemon zest until well blended. Set aside. In another bowl, mix the ingredients for the crumble with a fork until fine crumbs form.
Preheat the oven to 175°C. Roll out the dough and line a lightly greased pie dish (24 to 26 cm) with it. Form a 2-3 cm high rim.
Place the blueberries in the pastry shell and spread the liquid sour cream mixture on top. Spread smoothly. Crumble the crumble on top.
Bake the cake for 50 to 55 minutes.
Cool completely on a wire rack and cut.