Knead 250 g flour, 1 egg, fat in pieces and 1 pinch each of salt, pepper and nutmeg into a smooth dough. Cover and chill for about 30 minutes.
Clean the leek, wash thoroughly and cut into rings. Steam covered in little boiling salted water for about 3 minutes. Drain. Remove sausage from skin and dice. Grate cheese
Roll out the dough on a little flour until round (approx. 30 cm Ø). Line a greased quiche or springform pan (approx. 28 cm Ø) with it. Press the dough up at the edge, prick more often. Pre-bake in a hot oven (electric cooker: 200 °C/circulating air: 175 °C/gas: level 3) for approx. 10 minutes
Whisk 3 eggs and milk. Season with salt, pepper, nutmeg and paprika. Mix leek and sausage and spread on the dough. Pour egg milk over it and sprinkle with cheese. Bake in a hot oven at the same temperature for 40-45 minutes. Garnish with parsley if desired.