Ingredients

• 1 1/2 cups (3 sticks) unsalted butter, room temperature
• 6 tablespoons chopped hazelnuts
• 1 1/2 tablespoons Sherry wine vinegar
• 1 tablespoon chopped fresh thyme
• 2 teaspoons crushed black peppercorns
• 1 garlic clove, minced
• 3/4 teaspoon salt
• 9 ounces thinly sliced prosciutto, chopped
• 3 green onions, chopped
• Neck, heart, and gizzard reserved from one 16- to 18-pound turkey
• 3 large shallots, finely chopped
• 1 bay leaf
• 1 cup dry white wine
• 1 large fresh thyme sprig
• 1/2 teaspoon chopped fresh rosemary
• 4 cups low-salt chicken broth
• 1 16- to 18-pound turkey
• 1 onion, quartered
• 3 garlic cloves, peeled, halved
• 5 large fresh thyme sprigs
• 2 large fresh summer savory sprigs
• 1 tablespoon crushed black peppercorns
• 5 cups (about) low-salt chicken broth
• 1/4 cup all purpose flour

Instructions

1. Place butter in large bowl. Mix in hazelnuts, vinegar, thyme, crushed pepper, garlic, and salt. Mix in prosciutto and green onions.
2. For gravy base: Melt 2 tablespoons prosciutto butter in heavy large pot over medium-high heat. Add neck, heart, gizzard, shallots, and bay leaf; sauté until brown, about 20 minutes. Add wine, thyme, and rosemary; boil until liquid is reduced almost to glaze, about 3 minutes. Add 4 cups broth; bring to boil. Reduce heat to medium-low, cover, and simmer until giblets and neck are tender, about 1 hour. Discard bay leaf and thyme sprig. Transfer neck and giblets to work surface. Chop enough giblets to measure 1 cup. Remove meat from neck and chop. Combine neck meat and chopped giblets in bowl with broth from pot. (Prosciutto butter and gravy base can be made 1 day ahead. Cover and chill butter; bring to room temperature before using. Chill gravy base until cold, then cover and keep chilled.)
3. Melt 2 tablespoons prosciutto butter in heavy large pot over medium-high heat. Add neck, heart, gizzard, shallots, and bay leaf; sauté until brown, about 20 minutes. Add wine, thyme, and rosemary; boil until liquid is reduced almost to glaze, about 3 minutes. Add 4 cups broth; bring to boil. Reduce heat to medium-low, cover, and simmer until giblets and neck are tender, about 1 hour. Discard bay leaf and thyme sprig. Transfer neck and giblets to work surface. Chop enough giblets to measure 1 cup. Remove meat from neck and chop. Combine neck meat and chopped giblets in bowl with broth from pot. (Prosciutto butter and gravy base can be made 1 day ahead. Cover and chill butter; bring to room temperature before using. Chill gravy base until cold, then cover and keep chilled.)
4. For turkey: Set rack at lowest position in oven and preheat to 325°F. Rinse turkey inside and out; pat dry. Starting at neck end, slide hand between skin and breast, thigh, and leg meat to loosen skin. Set aside 1/4 cup prosciutto butter for gravy. Spread 1 cup prosciutto butter over turkey meat under skin. Spread 1 cup prosciutto butter over outside of turkey. Sprinkle turkey inside and out with salt and pepper; place on rack set in large roasting pan. Place onion and next 4 ingredients in main turkey cavity. Tuck wing tips under; tie legs together loosely. Roast turkey uncovered 1 1/2 hours. Tent turkey with foil; add 2 cups broth to pan. Roast until thermometer inserted into thickest part of thigh registers 175°F, occasionally basting with pan drippings and adding more broth to pan, about 2 hours longer. Transfer to platter; tent with foil. Let stand 30 minutes (internal temperature will increase 5 to 10 degrees).
5. Set rack at lowest position in oven and preheat to 325°F. Rinse turkey inside and out; pat dry. Starting at neck end, slide hand between skin and breast, thigh, and leg meat to loosen skin. Set aside 1/4 cup prosciutto butter for gravy. Spread 1 cup prosciutto butter over turkey meat under skin. Spread 1 cup prosciutto butter over outside of turkey. Sprinkle turkey inside and out with salt and pepper; place on rack set in large roasting pan. Place onion and next 4 ingredients in main turkey cavity. Tuck wing tips under; tie legs together loosely.
6. Roast turkey uncovered 1 1/2 hours. Tent turkey with foil; add 2 cups broth to pan. Roast until thermometer inserted into thickest part of thigh registers 175°F, occasionally basting with pan drippings and adding more broth to pan, about 2 hours longer. Transfer to platter; tent with foil. Let stand 30 minutes (internal temperature will increase 5 to 10 degrees).
7. Strain pan juices into 8-cup measuring cup; spoon fat off top. Add reserved gravy base. Add enough chicken broth to mixture to measure 5 cups total. Melt reserved 1/4 cup prosciutto butter in heavy large pot over medium-high heat. Add flour; whisk 1 minute. Gradually add pan-juice mixture, whisking constantly. Boil, whisking frequently, until gravy is very slightly thickened, about 5 minutes. Season with salt and pepper. Serve turkey with gravy.