Mustard and Rosemary Roast Turkey

Name: Mustard and Rosemary Roast Turkey
Ingredients: 1/4 cup Dijon mustard; 2 tablespoons extra-virgin olive oil; 4 garlic cloves, finely grated; 2 tablespoons finely chopped rosemary; 2 tablespoons kosher salt; 2 teaspoons black pepper; 1 (12-pound) turkey, cut into breasts, wings, and legs/thighs (have your butcher do this); 1 large onion, halved and thinly sliced; 1/2 cup dry white wine; 1 stick unsalted butter; 1/2 cup onion, finely chopped; 1 teaspoon freshly ground black pepper; Kosher salt; 1/2 cup all-purpose flour; 2 teaspoons port; 5 cups turkey stock