The secret to delicious gravy is a homemade stock, which you can prepare while the turkey roasts in the oven.
Make turkey stock while turkey roasts: Trim fat and membrane from giblets. Rinse giblets and neck; pat dry. Add to roasting pan with turkey, and roast until browned, about 30 minutes. Remove giblets and neck from pan; set aside.
Bundle together thyme, parsley, and rosemary, and tie with kitchen twine to make a bouquet garni; set aside.
Melt butter over medium-high heat in a large (4-quart) saucepan. Add celery, carrot, leek, and onion; cook, stirring occasionally, until just browned, 5 to 10 minutes. Reduce heat to medium; add giblets, neck, bouquet garni, pepper corns, bay leaf, and 4 cups water. Cover; bring to a boil. Uncover; reduce heat to medium-low. Cook until liquid reduces to about 3 cups, 50 to 60 minutes.
Pour stock through a large fine sieve set over a clean large saucepan. Reserve giblets and neck, and discard vegetables. Return stock to stove, and keep warm over medium-low heat. Coarsely chop giblets, and shred neck meat off the bone with a fork; set aside.
Make gravy when turkey comes out of the oven: Pour juices from roasting pan into a fat separator; reserve pan. Let juices separate, about 10 minutes.
Deglaze pan: Set the pan on stove top across two burners; add wine. Bring to a boil over medium-high heat, scraping up browned bits on bottom with a wooden spoon. Reserve deglazing liquid.
Add 3 tablespoons reserved pan fat (from top of separator) or butter to a clean large saucepan, and place over medium-low heat. Add flour to make a roux, whisking vigorously to combine. Cook, whisking, until flour is deep golden brown and fragrant, about 7 minutes. Whisking vigorously, add stock in a steady stream to roux. Bring mixture to a boil, then reduce heat to a simmer.
Add reserved deglazing liquid, pan juice (from bottom of separator), giblets, and neck meat to mixture. Return to a simmer; cook, stirring occasionally, until mixture is thickened, about 20 minutes.
Pour gravy through a fine sieve set over a large saucepan; discard giblets and neck meat, if desired. Keep warm on low until ready to serve (up to 30 minutes); season with salt and pepper.