Finely chop the onion. Fry 1/2 onion in a pan. Add finely chopped mushrooms, salt and fry for 20 minutes.
Melt the butter in a saucepan and fry the other half of the onion. Pour in rice, fry for 3 minutes. Pour in wine and stir until rice absorbs. Bring the broth to a boil and pour in small portions into the rice, adding the next when the previous one is absorbed. Before the last portion, add the mushrooms and mix.