Peel and finely chop the onion. Heat the butter in a large saucepan along with a drizzle of extra virgin olive oil (to prevent the first one from burning). We poach the chopped onion over low heat until is translucent.
Meanwhile we prepare the mushrooms, that is, we clean them with a damp cloth and we chop them up. Add to the saucepan, season to taste and fry for a couple of minutes or until reduced by half. Add the rice and stir so that all the grains are well impregnated with fat.
Next we add the white wine and stir again while the alcohol is absorbed and evaporated. At the same time we put the broth to heat and keep it at a constant temperature (without boiling) throughout the process.
When the wine has evaporated and the broth is hot, we lower the heat (medium-low) and begin to add the broth. We do it little by little, stirring the rice frequently to release its starch. When the rice looks dry, add more broth and proceed like this for 15-16 minutes.
We taste the point of the rice and, if it is al dente (if it is not the case we cook it a little more), we turn off the heat. Add the grated Parmesan cheese and the liquid cream and stir. We let stand for a couple of minutes with the saucepan covered, during which time the risotto will finish cooking.
For an extra point of flavor and texture, we serve the mushroom risotto with cheese flakes Parmesan or parmesan grated on the surface and a few turns of ground black pepper. We can also decorate it with chives or chopped fresh parsley.