Melt 175 g butter in a saucepan. Coarsely chop the walnuts. Mix 250 g flour, 125 brown sugar, 2 tsp cinnamon, 1 pinch of salt and 200 g walnuts in a bowl. Add hot butter all at once and knead into crumbles with the dough hooks of the hand mixer. Let it cool down
Mix 250 g butter, 200 g brown sugar, 2 teaspoons cinnamon, vanilla aroma, nutmeg, lemon peel and 1 pinch of salt with the whisk of the hand mixer for about 5 minutes until creamy. Weigh 50 g flour. Add the eggs one after the other, alternating with some of the weighed flour and stir well
Peel the bananas, crush them finely with a fork and stir into the egg-fat mixture together with the yoghurt. Mix 200 g flour and baking powder and add 200 g walnuts at the end. Grease a fat pan (32 x 38 cm) and dust with flour. Spread the dough on it. Spread crumbles on top and bake in the preheated oven, mid-height, (electric oven: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) for 30-35 minutes (may still be a little moist when you test the dough with the sticks!). Let the cake cool down in the fat pan on a cake rack
Caramelise the white sugar in a wide pot. Remove the pot from the heat, briefly stir in 10 g butter, add cream and mix well. Pour into a metal bowl and let it cool down. Stir in between if necessary. Cut cake into pieces, add caramel sauce