In a large pot over medium heat, melt butter. Add onion, carrots, celery and mushrooms. Sauté until onions are translucent and mushrooms have browned, 3 to 5 minutes. Add garlic, salt, pepper, thyme and nutmeg. Stir in until garlic releases its fragrance, about 30 seconds.
Add wine if using and deglaze pan for 2 to 3 minutes. Add stock and cook on medium low heat until celery and carrots are tender, 5 to 10 minutes.
Add rice and cream. Continue to cook until soup thickens slightly. Garnish with parsley.