Strain the turkey drippings through a fine mesh sieve into a large saucepan. Set aside 1 cup of the drippings in a bowl. Stir white wine, rosemary, and black pepper into the drippings in the saucepan, and bring to a simmer over medium-low heat. Simmer for about 20 minutes to cook off the alcohol and blend the flavors. Whisk cornstarch into the drippings in the bowl, and whisk the cornstarch mixture into the hot gravy. Allow the gravy to simmer until thickened, about 3 minutes. Stir in salt to taste; strain out any large pieces of rosemary before serving.