Melt butter in large Dutch oven over medium-high heat. Cook onions, celery and turkey carcass until lightly browned, about 5 minutes. Add wine and chicken broth and simmer over medium-low heat for 1 hour. Strain broth, discarding solids.
For the soup.
Wipe out Dutch oven and toast rice over medium heat until rice begins to pop, 5 to 7 minutes. Stir in turkey broth, carrots, thyme and baking soda and bring to boil. Reduce heat to low and simmer, covered, until rice is tender, about 1 hour.
Whisk flour and cream in bowl until smooth. Slowly whisk flour mixture into soup. Add turkey and simmer until soup is slightly thickened, about 10 minutes. Season with salt and pepper. Serve.