Combine flour, 2 pinches of salt, 1 egg and chopped butter and quickly knead into a smooth dough. Roll out on a floured work surface into the shape of the springform pan with 28 cm (approximately 11 inch) diameter. Lightly grease the pan and line with dough forming a 2 cm (approximately 3/4 inch) edge. Bake in a preheated oven at 200°C (approximately 400°F) on the center rack for about 10 minutes to prebake.
Cut pancetta into small cubes and fry in a pan. Peel the onion, dice and sauté in bacon grease. Chop sauerkraut coarsely and add to pan. Braise over low heat, covered for 10 minutes. Stir in creme fraiche and remaining eggs and season with salt and pepper.
Spread sauerkraut mixture on the pastry and bake in the oven on the center rack for 30 minutes. Remove from oven and serve warm.