Chop walnuts for the floor. Whisk butter and 75 g sugar with the whisk of the hand mixer until white and creamy. Stir in eggs. Mix flour, walnuts, except for a little bit for sprinkling, and baking powder. Alternately stir in with the milk
Put the dough into a greased springform pan (26 cm Ø) sprinkled with flour and smooth it down. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for approx. 30 minutes. Take out of the oven, carefully loosen the springform ring and put the cake in a cool place
Whip the cream until stiff, pouring in 50 g sugar. Mix sour cream and cream. Lift cooled cake from the bottom of the mould. Place a cake ring around the base and spread the sour cream on top. Chill the cake for at least 3 hours or overnight
Spread the porridge on the cake. Chill for about 5 minutes. Sprinkle with remaining walnuts and dust with cinnamon sugar
waiting time approx. 3 hours