Clean, wash and cut the leek into rings. Wash and halve the tomatoes. Drain sauerkraut well. Whisk eggs and sour cream. Season with pepper and salt if necessary.
Heat 1 tablespoon of oil in a frying pan. Fry the sauerkraut for 3-4 minutes. Add leek, diced ham and tomatoes and fry for about 5 minutes. Season with salt and pepper and let it cool down a bit.
For the dough, mix quark, milk, 4 tablespoons of oil and 1 pinch of salt. Mix flour and baking powder and add. Knead everything with the dough hooks of the mixer to a smooth dough. Grease a tart mould with a lifting base (24 cm Ø).
Roll out the dough into a round shape (approx. 26 cm Ø), place in the tin and press down at the edges. Spread the sauerkraut and ham mixture on top. Pour egg icing over it. Bake in the preheated oven (electric cooker: 200 °C/circulating air: 175 °C/gas: see manufacturer) for approx. 35 minutes.