How to Make It
Soak the porcini in the boiling water until softened. Drain, reserving the liquid; chop the mushrooms.
Heat the oil in a large saucepan. Add the onion and cook over moderately high heat until slightly softened, 2 to 3 minutes. Add the mushrooms and stir briefly. Add the rice, bay leaves, pepper, stock and the reserved porcini soaking liquid and bring to a boil. Reduce the heat to low, cover partially and simmer for 10 minutes.
Add the potatoes and carrots and bring to a boil. Cover partially and simmer over moderately low heat until the rice and vegetables are tender, about 30 minutes. Add the salt and simmer for a few minutes more. Ladle the soup into bowls and pass the cheese and parsley at the table.