For the dough, process all the ingredients into a smooth dough. Please only knead the dough for a maximum of 6-7 minutes, as you can knead over spelled dough and then the dough will not rise so nicely. Then cover and let the dough rise in a warm place for about 30 minutes.
Roll out the dough and line a baking pan (approx. 25 x 35 cm) with it. Either grease the baking pan or line it with baking paper. Let the dough rest, covered, for another 10 minutes.
For the topping, cut the onions into rings and dice the apple and smoked tofu.
For the topping, mix all the ingredients together well in the mixer. If necessary, season again to taste.
Spread the onion rings, apple and smoked tofu cubes on the dough. Scatter the walnuts on top and distribute the icing evenly over the topping. Bake the onion cake at 180 ° C for about 35 minutes (middle rack).
If you want to enjoy the onion cake warm, you should let the onion cake rest for about 5-10 minutes before slicing. The onion cake also tastes very good cold and can therefore be taken very well (e.g. to school, university or work, as well as to a picnic, etc.).
As a main course, the onion cake is enough for 6 large pieces. As a starter for 12 pieces.