Clean the mushrooms and cut them in slices. Peel the onion and cut into rings. Sauté both in a little heated oil until the liquid of the mushrooms evaporates and the onions are a little soft. Deglaze with cream and season with salt and pepper. Stir in a little parsley and bring everything to the boil. If desired, thicken the sauce with a light sauce thickener.
Arrange on plates and serve with the rice.
This fits e.g., breaded schnitzel, fish fingers or just a green salad.