Cook the pasta in plenty of boiling salted water for about 10 minutes. Drain on a sieve. Clean and wash the leek and cut into fine rings. Peel and dice the onion. Clean and wash the mushrooms and halve or quarter (depending on size).
Heat oil in a large pan. Squeeze the sausage meat out of the skin in dumplings into the hot fat. Fry for about 5 minutes, turning. Add onion and leek and fry with. Pour in milk, bring to the boil and simmer for about 5 minutes. Thicken slightly with sauce thickener. Season to taste with salt and pepper. Fold in the pasta. Warm up briefly. Wash, chop and sprinkle the parsley.