Knead the flour, butter in pieces, 1 egg and 1/2 teaspoon salt first with the dough hooks of the hand mixer, then briefly with your hands to a smooth shortcrust pastry. Grease a springform pan (26 cm Ø). Roll out the dough round (approx. 32 cm Ø) on a floured work surface.
Line the mould with the dough, prick the dough base several times with a fork and chill the mould for about 30 minutes.
In the meantime clean, wash and cut the leek into rings. Heat the oil in a large pan. Sauté the leeks for 2-3 minutes, turning them over. Season with salt, pepper and a little nutmeg. Wash the fish, dab dry and cut into cubes of approx. 3 x 3 cm.
Mix 3 eggs, crème fraîche and mustard. Season with salt, pepper and nutmeg.
Pre-bake the dough in a preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: see manufacturer) for approx. 15 minutes. Remove the mould from the oven. Spread leek and salmon on top. Pour egg-cream-fraîche over it.
Grate the cheese and spread on top. Bake at the same temperature for 35-40 minutes. Remove the tart. Serve with radicchio-dill salad.