Preheat oven to 350 degrees F. Remove top rack. Prepare compound butter by combining butter and dressing mix in a small bowl; stir with spoon until well incorporated. Adjust seasoning with freshly ground black pepper; set aside. Melt 1 tablespoon of compound butter in medium skillet. Toss apple cubes in melted butter and cook approximately 2 minutes to gently caramelize. Remove apple cubes and set aside. In same pan melt half of compound butter over medium heat, reserving remaining compound butter for turkey. Add onion and rosemary; cook until lightly browned. Add Italian sausage meat and cook 10 minutes, until soft and golden. Scrape sausage mixture into large mixing bowl, add apple and cornbread pieces; toss to combine. Season well with salt and pepper. In separate bowl, whisk egg, cream and 1/2 cup stock; pour liquid over cornbread mixture. Stir stuffing together; set aside. Rinse turkey thoroughly inside and out with cold water; pat dry with paper towels. Sprinkle cavity and skin liberally with salt and pepper. Using fingers, gently lift skin from breast and rub dressing mix compound butter under skin, massaging breast meat as you go. Spread remaining compound butter over exterior of skin, covering wings, legs and any gaps. Stuff bird with prepared stuffing. Truss with kitchen twine or simply cross legs over and secure with twine. Position turkey on rack in large roasting pan; transfer to oven. Roast turkey approximately 3 hours, until instant-read thermometer inserted into meaty part of thigh registers 170 degrees F (thigh juices will run clear when pricked with knife, 15 minutes per pound). If legs or breast brown too quickly during roasting, cover with foil. Remove turkey from oven; transfer to serving tray to rest while making gravy. Skim off most fat from pan drippings with spoon and position roasting pan across two burners over medium-high heat. Using wooden spoon, scrape up browned bits stuck to bottom of pan. Whisk in flour, stirring as it thickens to prevent lumps. Pour in remaining 2 1/2 cups stock, 1/2 cup at a time, stirring constantly to blend and prevent lumps. Bring to a simmer; season with salt, pepper and squeeze of lemon juice to brighten flavors. Simmer for 5 minutes; strain to remove solids. Serve with turkey and stuffing.