Fennel and Citrus Roasted Turkey with Gravy

Name: Fennel and Citrus Roasted Turkey with Gravy
Ingredients: One 12-pound turkey; 2 lemons; 1 orange; 1 head fennel, quartered, fronds reserved for butter and garnish; 1 stick (8 tablespoons) unsalted butter, softened; Kosher salt and freshly ground black pepper; 1 bunch fresh thyme; 1 cup chicken or turkey stock; 6 tablespoons unsalted butter; 1 tablespoon fresh thyme leaves, chopped; 2 shallots, finely chopped; 1/3 cup all-purpose flour; 2 tablespoons dry Marsala wine; 3 cups turkey or chicken stock; Pan juices from roasted turkey (fat separated); 1 teaspoon sugar, optional