01 - Preheat the oven to 180°C (350°F) and grease a round cake pan.
02 - In a bowl, mix the flour, sugar, butter, egg, baking powder, and salt until a dough forms. Press this mixture into the bottom of the prepared cake pan.
03 - In another bowl, combine the quark, sugar, eggs, vanilla extract, and lemon zest. Mix until smooth and pour over the cake base.
04 - Sprinkle the fresh blueberries evenly on top of the quark layer and gently press them in.
05 - For the crumble, combine the flour, sugar, butter, and cinnamon in a bowl. Use your fingers to mix until crumbly. Sprinkle the crumble over the blueberries.
06 - Bake in the preheated oven for 45 minutes or until golden brown and set.
07 - Allow the cake to cool before slicing and serving.