Cut pumpkin into large pieces and cook in boiling salted water for about 20 minutes until soft. Drain and puree finely. Let cool off.
Cream 250 g butter, 200 g sugar, 1 pinch of salt and vanilla sugar with the whisk of the hand mixer. Stir in the eggs one by one. Mix 200 g flour, spelt flour and baking powder and stir in alternately with pumpkin puree.
Fill onto a greased, floured baking tray (approx. 24 x 38 cm) and smooth it down.
Knead 150 g sugar, 150 g butter, 250 g flour and cinnamon first with the dough hooks of the hand mixer, then with your hands to crumbles. Knead the oat flakes. Spread the crumbles on the dough. Bake in a preheated oven (electric cooker: 175 °C/ circulating air: 150 °C/ gas: see
manufacturer) bake for about 35 minutes. Take out and let cool down.
Wash the lemon, grate dry and grate half of the peel. Mix the lemon peel, apple sauce and mascarpone. Use the rest of the lemon for other purposes. Cut cake into pieces and serve with mascarpone cream.