Skin the onions and garlic. Then finely dice both.
Heat the olive oil in a pan and steam both in it until translucent. Then pour in the cream, the vegetable stock and the white wine and season with salt, pepper and the herbs. Let the whole thing simmer over a low heat for 7-8 minutes. Stir in the chopped walnuts and simmer for another 3-4 minutes.
In the meantime, prepare the tortellinis according to the instructions on the packet.
Season the sauce again to taste. Stir the parmesan into the sauce. Bring to the boil again briefly.
Spread the tortellinis on plates and pour the sauce over them.