Chop up a little onion, parsley, celery, and carrot together, and put them on the fire with two tablespoons of good olive-oil. 

When this sauce is colored, add two tablespoons of tomato paste, thinned with hot water (or a corresponding quantity of tomato sauce). Season with salt and pepper. 

Cut the mushrooms into small pieces, and add them to the sauce. Cook for twenty minutes over a medium fire. Put on one side and prepare the rice as follows:

Fry the rice with a lump of butter until dry; then add hot water, a little at a time, and boil gently. When the rice is half cooked (after about ten minutes) add the mushrooms and sauce, and cook for another ten minutes. 

Add grated Parmesan cheese before serving.