Melt 250 g butter and let it cool down. Preheat oven (electric cooker: 180 °C/circulating air: 160 °C/gas: see manufacturer). Grease a fat pan (deep baking tray; approx. 32 x 39 cm) and dust with corn flour.
Mix 400 g corn flour, almonds and baking powder. Cream brown sugar, vanilla sugar and eggs with the whisks of the mixer. Alternately stir in flour mixture, liquid butter and milk. Put the dough on the fat pan and smooth it down. Bake in a hot oven for about 20 minutes. Let it cool down on a cake rack.
Wash and clean the strawberries and, depending on the size, leave them whole or halve them. Mix cream and sugar. Whip the cream and sour cream with the whisk of the mixer in 2 portions until stiff, also allow the sugar mixture to trickle in portions. Spread the cream on the dough. Spread strawberries on top. Warm the jam in a pot and spread on the strawberries. Put in a cool place for about 1 hour.
Remove the pistachios from their shells and chop them roughly. Sprinkle over the cake.