Preheat the oven to 375 F and grease a tart pan with removeable bottum or a 9 inch springform pan.
Beat the soft butter and sugar together with the mixer until frothy. Mix in the egg.
Then combine the rye flour with the cardamom, baking powder and add to the egg mixture! Combine everything into a batter. The dough should no longer be too sticky. If necessary, just add a little more flour.
Press the dough into the cake pan with your fingers forming an edge around 2 cm up the sides.
Optional: Prick the tart all over with a fork and blind bake at 375 F for about 8 minutes.
For the filling mix all ingredients for the filling with the hand mixer - apart from the the blueberries, then pour into the blind baked and cooled or unbaked crust and sprinkle with the blueberries.
If you now notice that the edge of the dough is too high, simply press it down a little.
Bake the tart at 375 for 25 - 30 minutes for a 9 inch / 23 cm pan - if you have a 28 cm/ 11 inch tart pan, the filling takes less time to set. If you have prebaked it , it will be done after 25 minutes for sure. If you see your crust is browning too quickly, cover with aluminum. The filling will be a bit jiggly in the middle when you take it out, just like a cheesecake. It becomes firmer as it cools.