Pour the flour out onto a work surface, mix with salt and make a well in the center. Cut the cold butter into small pieces and distribute around the flour. Beat the egg and pour into the center, along with 2-3 teaspoons of lukewarm water. Mix all the ingredients with a pastry knife until crumbly, then knead by hand to form a smooth dough. Form into a ball, wrap in plastic wrap and refrigerate for 30 minutes.
Mix together the milk and eggs. Cut the bacon into strips. Peel the onion, cut in half and chop. Rinse the apple, quarter, remove the core and cut into slices. Drain the sauerkraut, squeeze out the excess liquid and chop. Rinse the parsley, shake dry, pluck off the leaves and chop.
Roll out the dough on a lightly floured surface and line the greased baking dish with it.
Fry the bacon in a large skillet briefly, add the onion and apple and fry for 2 minutes. Remove from the heat and mix in a large bowl with the milk, eggs and parsley and season with salt and pepper. Spread the filling on the dough, sprinkle with grated Emmentaler and bake on the bottom shelf of a preheated oven at 200°C (approximately 400°F) until golden brown, about 30 minutes. Serve warm or cold as desired.