In a medium or large pot simmer 4 cups of the turkey stock with a few sprigs fresh sage, thyme, 2 teaspoons salt (if using my homemade stock with no salt, use less if your stock is salted) and black pepper to taste and simmer 15 minutes. Discard the herbs.
Once it’s ready, in a blender add remaining 1 cup cold broth with 2/3 cup flour and the Bell's poultry seasoning and blend until smooth.
Add 2 cups of the boiling turkey stock into the blender to temper and blend again, then pour into the pot with the boiling stock.
Add the pan drippings from the turkey at this point and simmer, whisking on low heat until thickened, about 5 to 10 minutes. Taste for salt and adjust as needed.