Cut the cold butter into pieces and place in a large mixing bowl.

Add sugar and vanilla sugar.

Pour flour and baking powder, and knead the crumbly dough by hand.

Divide the dough into two parts, larger and smaller (the larger part is approximately two thirds, and the smaller one is one third of the dough).

Wrap both doughs in transparent foil, then put the larger part in the fridge and the smaller part in the freezer for half an hour.

For the filling, put Greek yogurt, sour cream, sugar and vanilla sugar in a bowl.

Add the flour and grated lemon zest, then combine everything with a whisk and set aside.

In another bowl, beat the egg whites with a mixer until stiff.

Add the egg white snow to the filling several times and combine everything with a whisk.

After half an hour, grease and flour a 13x8 inches baking pan.

Take the bigger dough out of the fridge and spread it in the pan using a glass.

Pour the filling onto the dough, then flatten it.

Arrange the washed and dried blueberries on top of the filling, then press them lightly with your finger.

Take the dough out of the freezer, then grate it over the filling and blueberries on a larger ribeye.

The pie is baked in an preheated oven at 350 degrees for 30 minutes.

Sprinkle the cooled pie with powdered sugar before cutting and serving.