Cut the vanilla pod lengthwise and scrape out the pulp. For the crumbles, knead 360 g flour, 120 g sugar, 240 g soft fat and vanilla pulp into crumbles. Drain the apricots and let them drain well. For the dough, chop the pistachios coarsely. Mix 250 g soft fat, 250 g sugar and lemon zest with the whisk of the hand mixer until creamy. Stir in the eggs one after the other. Mix 200 g flour, cornstarch and baking powder and stir in briefly, alternating with buttermilk.
Fold in the pistachios. Pour the dough onto a greased and floured baking tray (33 x 39 cm) and smooth it down. Spread the apricots evenly on top. Sprinkle crumbles over it. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for approx. 40 minutes. Cut the cake into 24 pieces and dust some with icing sugar if necessary.