Melt butter in a large skillet over medium-high heat. Add celery and onion; cook 4 minutes or until almost tender. Add mushrooms and garlic; cook 2 minutes.
Combine mushroom mixture, broth, and next 6 ingredients in a 5 quart crockpot.
Cover and cook on LOW for 5 to 6 hours or until rice is tender. Stir in whipping cream. Garnish, if desired.
Test Kitchen Secret Roasted garlic-flavored chicken broth is the secret to fantastic flavor in this soup. If you have a hard time finding it, just ask your grocer to order some for you. If it is unavailable, double the minced garlic.