Mix the baking mix and 400 ml of lukewarm water with the dough hooks of the hand mixer at the lowest setting. Then knead for approx. 3 minutes at the highest setting to a smooth dough. Cover the dough and let it rise in a warm place for about 15 minutes. Then knead with your hands on some flour, form into a ball and let it rise for another 30 minutes.
Clean and wash the leek and cut it into rings of about 2 cm thickness. Heat the oil in a large pan. Brown the ground pork in it until crumbly, take it out. Steam the leek, if necessary in portions, in the frying fat for about 10 minutes. Add the minced meat again and stir in the crème fraiche. Season to taste with salt, pepper and nutmeg
Knead the dough on some flour again. Roll out round (approx. 36 cm Ø; 1 cm thick). Line a greased baking tray (approx. 32 cm Ø) or springform pan (28 cm Ø) with the dough, pressing down on the edges. Spread the leek-milk mixture over it. Grate the cheese and sprinkle over it. Bake in the preheated oven (electric oven: 200 °C/circulating air: 175 °C/gas: level 3) on the lowest shelf (gas: see oven manufacturer) for 40-50 minutes. If necessary, cover after approx. 30 minutes