Preheat oven (electric cooker: 175 °C/circulating air: 150 °C/gas: see manufacturer). Line a rectangular springform pan (24 x 36 cm) with baking paper. Grind the macadamia nuts finely in the universal chopper, then mix with polenta, starch and baking powder.
Cream butter, sugar and lemon zest with the whisks of the mixer. First add eggs one after the other, then yoghurt and lemon juice. Quickly stir in the polenta mixture. Smooth the dough in the tin and pre-bake in a hot oven for approx. 15 minutes.
In the meantime, select the blackberries, wash and drain them if necessary. Spread on the cake. Continue baking for about 15 minutes.
Take the cake out of the oven and let it cool down. Dust with icing sugar for serving.