Rinse giblets and neck (chill liver airtight to add later, save for other uses, or discard). In a 5- to 6-quart pan, combine giblets, neck, onions, carrots, celery, and 1 cup water. Cover and bring to a boil over high heat; reduce heat and simmer for 15 minutes. Uncover and stir often over high heat until liquid has evaporated and giblets and vegetables are browned and begin to stick to pan, 12 to 15 minutes longer.
Add 1 quart broth and pepper; stir to scrape browned bits free. Cover, reduce heat, and simmer until gizzard is tender when pierced, 1 to 1 1/2 hours. If desired, add liver; cook 10 minutes longer.
Pour broth through a fine strainer into a bowl. Measure and, if needed, add water to make 1 quart. Discard vegetables. If desired for gravy, pull meat off neck and finely chop, along with giblets and liver; otherwise discard neck, giblets, and liver.
In the 5- to 6-quart pan (no need to wash), blend cornstarch with 1/3 cup water until smooth. Add the 1 quart broth, plus the chopped neck meat, giblets, and liver if using. Stir over high heat until boiling, 3 to 5 minutes.
When turkey is done, remove rack and bird from pan; skim off and discard fat from pan juices. Add remaining 2 cups broth to roasting pan and stir over low heat, scraping browned bits free. Add mixture to gravy and stir over high heat until boiling. Add salt to taste.
Wine Gravy: Follow recipe for Savory Gravy (preceding), but in step 5 replace the last 2 cups broth with 2 cups Chardonnay or other dry white wine, tawny port, dry sherry, or dry madeira.
Nutritional analysis per 1/2 cup without giblets and neck meat.