Knead 250 g flour, 1 pinch of salt, 2 tbsp. oil, egg and approx. 100 ml lukewarm water with the dough hooks of the hand mixer to a smooth dough. Then I knead with my hands for about 12 minutes and beat the dough more often on the work surface.
Wrapped in foil and left to rest at room temperature for about 1 hour.
Clean or peel and wash the soup vegetables. Peel the onion. Dice everything finely. Roast the pine nuts and take them out. Fry the soup greens and onion briefly in 1 tbsp. hot oil. Now I add the frozen spinach and 3 tablespoons of water and cook everything covered for about 12 minutes.
Season with salt, pepper and nutmeg. Cool in a sieve and drain.
I roll the dough out to a rectangle 1/2 cm thick. Then I pull the dough larger (approx. 45 x 60 cm) over the backs of my hands until it becomes so thin that you can see the pattern of the cloth through the dough.
The thinner, the better the result will be later.
Melt the butter and spread a good half of it thinly on the dough. Sprinkle the bottom two thirds of the dough with breadcrumbs, leaving about 2 cm of edge free. Spread the vegetables and 3 tbsp. pine nuts on the breadcrumbs.
Turn the sides slightly. Roll up the dough from the narrow side using the tea towel. With the seam facing downwards, place it diagonally on a baking tray lined with baking paper. Coat with the rest of the butter.
Bake in a hot oven (electric cooker: 200 °C/circulating air: 175 °C/gas: level 3) for 30-35 minutes.
In the meantime I peel the horseradish and grate it finely. Then I mix it with quark, yoghurt and the herbs and season the sauce with salt and pepper. Cut the strudel into pieces and arrange on plates.
Sprinkle with remaining pine nuts. Serve with the horseradish sauce.