Preheat oven (electric cooker: 200°C/circulating air: 175°C/gas: level 3). Grease a large square casserole dish. Knead dumpling dough and egg yolk with the dough hooks of the hand mixer. Press the bottom of the dish with your hands and press the rim of the dish slightly upwards.
Pre-bake in the hot oven on the lowest shelf for about 30 minutes.
In the meantime clean, wash and cut the leek into rings. Heat the oil in a large pan. Fry the minced meat and minced pork together in the pan until crumbly. Season with pepper and a little salt. Take out.
Sauté the leek in the frying fat. Season with salt, pepper and nutmeg. Sprinkle with flour and sweat. Add 200 ml water and cream while stirring. Stir in processed cheese. Bring to the boil and simmer for about 5 minutes.
Fold in the mince. Season everything again with salt and pepper.
Remove the mould from the oven. Sprinkle the bottom with breadcrumbs. Spread the chopped mass on top. Sprinkle with cheese and bake at the same temperature for about 30 minutes.