This basic recipe will give a better result using the turkey stock. Remember to warm your gravy boat or serving pitcher with hot water a few minutes before you need it to serve the gravy. Dry it before adding the gravy.
In a medium saucepan, bring 4 cups of stock to a boil. Remove from heat and keep warm.
Melt butter in a large heavy saucepan over medium heat. Whisk in flour and cook, whisking, for 1 minute. The roux will become smooth and golden brown. Keep whisking!
Within 2-3 minutes it will be the color of cafe au lait (golden brown) and smell slightly toasted. Gradually whisk in the warm stock and bring to a boil. Lower heat so the gravy is at a bare simmer.
Add the bay leaves, mushrooms and Madeira and let simmer until grav is reduced by half. Remove the bay leaves and the mushrooms by a slotted spoon. Keep warm until turkey is finished.
Transfer the turkey to a carving board and strain the drippings from the pan into a measuring cup. Skim the fat, add enough water to measure 1 cup.
Place the roasting pan over two burners on medium high heat. Add the drippings mixture and deglaze the pan, stirring and scraping any browned bits with a wooden spoon. Strain into the gravy and simmer until slightly thickened, 10 minutes. Season to taste and serve.