cornbread stuffing: Melt 8 tablespoons of the butter in a large, heavy skillet, add the chopped onions and cook over moderate heat for 6 to 8 minutes, or until they color lightly.
Scrape them into a large mixing bowl.
Add the sausage to the skillet, now set over medium heat, and break the meat up with a fork as it cooks.
When the meat is lightly browned, transfer it to a sieve set over a small bowl and let the fat drain through.
Meanwhile, again in the same pan, melt the remaining 2 tablespoons of butter and, when the foam subsides, add the turkey liver.
Brown it over high heat for 2 to 3 minutes, then chop it coarsely and combine with the onions in the bowl.
Add the drained sausage meat, cornbread crumbs, salt, a few grindings of black pepper, the thyme and parsley.
With a large spoon, gently stir the ingredients together, then moisten the stuffing with the Madeira or sherry and cream.
Taste for seasoning.
Turkey: Preheat the oven to 350°.
Wash the turkey under cold running water and dry it thoroughly inside and out with paper towels.
Rub the inside of the turkey with the salt and a few grindings of pepper, and fill the body and breast cavities loosely with the stuffing, closing the openings with skewers or sewing them with thread.
Truss the bird securely.
With a pastry brush or paper towel, brush the outside of the turkey with a few tablespoons of the melted butter and sprinkle it with salt.
Place the bird on a rack in a shallow roasting pan and scatter the onions around it in the bottom of the pan.
Roast the turkey uncovered in the middle of the oven for about 2 hours, basting it every 15 minutes or so with the rest of the melted butter and with the drippings that accumulate in the pan.
To test for doneness pierce the thigh of the bird with the tip of a small, sharp knife.
The juice should spurt out a clear yellow; if it is slightly pink, roast the bird for another 5 to 10 minutes.
GRAVY: While the turkey is resting, make the gravy.
Pour off all but about 3 tablespoons of fat from the roasting pan and stir the flour into the pan.
When the flour is thoroughly absorbed, add the cup of water or stock.
Bring to a boil over high heat, stirring constantly with a wire whisk and incorporating into the liquid the brown sediment on the bottom and sides of the pan.
When the sauce is quite thick, beat in the cream.
If you prefer the gravy thinner, add a little more cream.
Taste for seasoning and pour into a heated gravy boat.
The gravy may be strained if you like.