- Place turkey carcass in a large pot or Dutch oven and cover with water. Bring to a boil. Reduce heat to medium, cover, and simmer for 1 hour. Remove carcass and allow to cool. Separate turkey meat from the bones. Cut meat into bite-size pieces; discard bones. Reserve about 12 cups turkey broth in a large bowl. Save remaining broth for another use.
- Melt butter in another large pot or Dutch oven over medium heat; cook and stir onion, carrots, and celery in melted butter until tender, about 5 minutes. Stir flour into vegetable mixture; cook and stir until smooth, about 5 minutes. Gradually stir in about 1/3 the reserved turkey broth. Bring to a boil; cook and stir until thickened, about 2 minutes.
- Stir remaining turkey broth, turkey meat, half-and-half, fettuccine, stuffing, salt, chicken bouillon, pepper, and poultry seasoning into half-and-half mixture. Reduce heat to medium-low, cover, and simmer until noodles are tender, about 10 minutes more.