If goose is frozen, place it in the refrigerator overnight to thaw. Remove goose from the refrigerator, and let it stand at room temperature for 30 minutes. Heat oven to 400 degrees. Rinse goose inside and out with cold running water, and pat it dry with paper towels. Trim as much of the excess fat as possible from the opening of the cavity. Remove the first and second joints of the wings, and set them aside for use in making the stock.
With the point of a sharp knife, prick the entire surface of the goose skin, being careful not to cut into the flesh. Fold the neck flap under the body of the goose, and pin the flap down with a wooden toothpick. Generously sprinkle the cavity with salt and pepper, and insert 2 carrot halves, 2 celery-stalk halves, garlic, thyme, and sage. Using a piece of kitchen twine, tie the legs together. Generously sprinkle the outside of the goose with salt and pepper, and place it, breast-side up on a wire rack set in a large roasting pan.
Roast goose in the oven until it turns a golden brown, about 1 hour. With a baster, remove as much fat as possible from the roasting pan every 30 minutes. Reduce the heat to 325 degrees, and roast until the goose is very well browned all over and an instant-read thermometer inserted into a breast, not touching a bone, registers 180 degrees, about 1 hour after reducing the temperature.
Meanwhile, prepare goose stock, which will be used when making the gravy and the dressing. Trim and discard any excess fat from the wing tips, neck, and giblets, and place them in a small stockpot. Add 4 carrot halves, 4 celery-stalk halves, both onion halves, parsley, bay leaf, peppercorns, and enough water to cover the bones and vegetables by 1 inch (about 2 1/2 quarts water). Place the stockpot over high heat, and bring to a boil. Reduce heat to medium low, and simmer stock, skimming the scum as it forms, for 2 hours. Strain stock through a cheesecloth-lined strainer. Remove and discard the fat floating on the surface of the stock, and set the stockpot aside.
Remove goose from the oven, and transfer it to a cutting board that has a well. Let the goose stand 15 to 20 minutes.
Meanwhile, prepare the gravy. Pour off all the fat from the roasting pan, and place the pan over high heat. Pour in wine, and cook, stirring up any brown bits with a wooden spoon until the cooking liquid is reduced by three-quarters. Add 2 cups goose stock, and cook, stirring until the liquid is again reduced by three-quarters. Season with salt and pepper to taste. Stir in butter, and cook until slightly thickened. Pass the gravy through a cheesecloth-lined strainer into a gravy boat, and serve with the goose.