Gather the ingredients.

Preheat the oven to 350 F (175 C). Grease a large ring mold.

Beat the butter and sugar until light and creamy (about 5 minutes).

Turn the beater to the lowest setting and add the eggs, one by one.

Zest the lemons and squeeze out the juice. Set the lemon juice aside to use later. Add the lemon zest, quark, and milk to the butter mixture. Don't be alarmed if the mixture looks slightly curdled at this stage.

Sift the baking powder and flour into the batter and gently fold through the mixture.

Pour the batter into the ring mold. Arrange most of the blueberries on top of the batter (they will sink while cooking). Keep some blueberries aside to decorate the top of the cake later.

Bake the cake until a skewer inserted into the cake comes out clean, about 50 to 55 minutes.

Allow to cool in the mold on a wire rack for 1/2 hour and then invert on the rack (still in the mold) and allow to cool for 1 1/5 hours.

To make the lemon glaze, mix the powdered sugar and half the lemon juice in a bowl and whisk until completely lump-free. It should be opaque and pourable. Add a little extra lemon juice, if the consistency is too thick.

When the quark cake is stone cold, remove it from the mold and set the rack with the cake over a piece of wax paper or paper kitchen towels, for easy clean-up. Drizzle the cake with the lemon glaze, decorate with blueberries and finish with a dusting of powdered sugar.