Grease the fat pan (deep baking tray; approx. 32 x 39 cm). Preheat oven (electric cooker: 175 °C/circulating air: 150 °C/gas: see manufacturer). Wash, clean and drain gooseberries.
Put flour, oat flakes, 375 g butter in pieces, sugar, vanilla sugar and 1 pinch of salt into a mixing bowl. First mix slightly with the dough hooks of the mixer, then knead coarsely with your hands to crumbles.
Mix in gooseberries briefly.
Spread the crumble-berry mixture on the tray and press it down lightly with your hands. Bake in a hot oven for about 30 minutes. Let it cool down.
Whip the sour cream with the whisks of the mixer until thick and creamy. Fold the caramel spread into the sour cream. Cut the cake into approx. 6 x 6 cm pieces. Serve with caramel sour cream.