Wash the potatoes and boil in water for about 20 minutes. Peel and finely chop the onion. Drain the sauerkraut. Heat oil. Sauté sauerkraut and onion. Pour on 1/8 litre water, stir in stock.
Season with salt, pepper, paprika and sugar. Let it braise for about 10 minutes. Drain potatoes, rinse with cold water, peel. Press half of the potatoes through a potato press. Stir in egg yolk. Season with salt, pepper and nutmeg. Cut the remaining potatoes into slices. Grease a pieform (approx. 26 cm Ø). Smooth the mashed potatoes in it. Spread the sauerkraut on it and cover with potato slices. Grate cheese and sprinkle over the potatoes. Put butter in flakes on top.
Grease a pieform (approx. 26 cm Ø). Smooth the mashed potatoes in it. Spread the sauerkraut on it and cover with potato slices. Grate cheese and sprinkle over the potatoes. Put butter in flakes on top. Bake in the preheated oven (electric cooker: 200 °C/ gas: level 3) for about 20 minutes. Wash the chives and cut into small rolls. Serve the quiche sprinkled with a dash of crème fraîche and chives