Put flour, some salt, butter in pieces, paprika powder, dried oregano and 1 egg into a bowl and knead first with the dough hooks of the hand mixer, then with your hands to a smooth dough. Wrap the dough in foil and chill for about 30 minutes
Wash potatoes thoroughly and cook in boiling salted water for about 8 minutes. Clean and wash the chard, drain well and cut into small pieces. Peel onion and garlic and cut into fine cubes. Drain the potatoes, let them drain well and cut them into approx. 5 mm thick slices
Heat the oil in a large frying pan and sauté the onion and garlic. Add chard, fry everything for about 3 minutes and let it cool down briefly. Roll out the dough on a floured work surface until round (approx. 28 cm Ø). Grease a tart tin (24 cm Ø) and line it with the dough, pressing the edge down. Cut off the protruding edge
Mix milk and 3 eggs, season with salt, pepper and nutmeg. Put potatoes and vegetables into the form and pour the egg-milk over them. Grate cheese and spread it on the tart. Bake the tart in a preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: see manufacturer) for approx. 45 minutes. Take the tart out of the oven, let it cool down a little, remove from the mould and sprinkle with some paprika powder. Cut the tart into 12 pieces