Soak the porcini mushrooms in water. Then squeeze them well, but save the water.
Slowly toast the walnuts without oil at low temperature until they smell good. Remove from heat (otherwise they will toast and burn).
Wash the leeks and cut them into fine rings. Peel and finely chop the onion and garlic.
Cook linguine according to package directions until al dente. Add the leeks about 5 minutes before the end of the cooking time. Drain both through a sieve.
Crumble blue cheese and fold into pasta to melt.
Heat a little oil in a frying pan. Sauté onion and garlic until translucent. Add the mushrooms. Add walnuts.
Pour in soup and the collected mushroom water and simmer for 5-10 minutes.
In the meantime, mix whipping cream and milk and stir in cornstarch until smooth.
Thicken the sauce with it and let it boil down a bit.
Add the sauce to the pasta and serve in deep plates.