Heat oven to 350 degrees. For stuffing, cut bread into 1 inch pieces. Place on two baking sheets. Bake, stirring often, until lightly toasted, about 20 minutes. Cool. Toast nuts in a small skillet, stirring constantly, over medium heat, about 3 minutes, until golden. Remove from heat. Melt butter in large pan and add pancetta, cook and stir until lightly browned, about 10 minutes. Stir in onion and celery and cook until vegetables are crisp-tender, about 10 minutes. Stir in bread cubes, nuts, seasoning, salt, and pepper. Stir in enough turkey or chicken broth to moisten the whole mixture well but not to make it soggy. Transfer mixture to a well-buttered, deep baking dish. Refrigerate, covered, up to 2 days. Heat oven to 325 degrees. For turkey, rinse turkey thoroughly; pat dry. Place turkey on a flat rack in a shallow roasting pan. Brush with oil. Roast until a meat thermometer inserted deep in the thigh registers 170 degrees, about 3 hours. Cover the breast meat with foil if skin browns too quickly. Let rest 15 to 20 minutes; temperature should rise to 180 degrees. About 30 minutes before turkey is done, place baking dish with stuffing into the oven. Bake until heated through and top is a bit golden, 30 to 45 minutes. Keep warm. For gravy, transfer turkey to warm serving platter. Pour all pan drippings into a bowl and let stand so fat separates out. Skim off and discard all the fat that floats on the surface. Pour Marsala or wine into the roasting pan and boil hard while scraping up all the browned bits from the bottom of the pan. Stir in the defatted pan drippings and turkey broth; heat to a boil. Whisking vigorously, pour in the dissolved flour. Cook and stir until smooth, thick and mixture boils. Season with salt and pepper. Carve turkey into thin slices. Serve turkey with some of the gravy and stuffing.