Defrost the blackberries. Take off 100 g and puree finely. Cream fat, sugar, salt and vanilla sugar with the whisk of the hand mixer. Stir in the eggs one after the other. Mix 350 g flour and baking powder and stir into the fat-egg mixture alternately with milk.
Cut the dough in half. Stir pureed berries and 20 g flour into one half. Pour the light, then dark dough into a greased, flour-sprinkled ring cake tin (approx. 2.5 litres capacity) and bake in a preheated oven (electric range: 175 °C/ convection oven: 150 °C/ gas: see
manufacturer) bake for about 45 minutes. Remove from the oven and leave to cool in the mould for approx. 10 minutes. Turn out onto a cake rack and let it cool down.
In the meantime, stir the jam until smooth and mix with the remaining berries. Stir icing sugar with lemon juice until creamy and smooth and let it run over the cake. Sprinkle with lavender flowers. Fill the blackberries into the depression of the ring cake.