For the blueberry tart, cream butter with baking sugar and vanilla sugar until very fluffy. Separate the eggs, thoroughly mix in the yolks one at a time.
Sift cocoa with flour and, according to taste, with ground cinnamon and clove powder over the butter and stir in. Beat egg whites to snow and fold in carefully but still thoroughly.
Butter a 30 cm diameter tart pan and sprinkle with flour. Pour in the batter, sprinkle with the washed blueberries and bake the blueberry tart at 180 °C for about 30 minutes.