Brown onions, celery, and turkey carcass in butter. Add wine and broth. Simmer 1 hour. Strain.
Toast rice in wiped-out pot. Add broth, carrots, thyme, baking soda. Simmer until rice is tender, about 1 hour.
Whisk flour and cream. Stir into soup. Add turkey. Simmer until slightly thickened, about 10 minutes. Season and serve.