Remove any good pieces of turkey meat that you want to save for sandwiches, soup, or other meals, then break the remaining carcass into several pieces so it fits comfortably into a large stockpot. Add the bones, wing tips, skin, and any small scraps of meat still attached to the carcass.

Add the quartered onion, roughly chopped carrots and celery, crushed garlic cloves, bay leaf, and whole black peppercorns to the pot. There is no need to peel the carrots or finely chop the vegetables since everything will be strained out once the stock is finished.

Pour in enough cold water to cover the turkey bones and vegetables by about 1 inch. Try not to add more water than you need because the more water you use, the longer the stock will need to cook and reduce before it develops a rich turkey flavor.

Place the stockpot over medium to medium high heat and slowly bring the water to a simmer, then reduce the heat until you have a gentle simmer with an occasional bubble rather than a hard rolling boil.

Let the stock simmer gently, uncovered, for about 3 to 4 hours, checking it occasionally and adding a little water if necessary to keep most of the bones submerged. As everything cooks, the water will pull flavor from the turkey, bones, connective tissue, vegetables, and seasonings while slowly reducing and becoming more concentrated.

Taste the stock once it has developed a rich turkey flavor, but don't automatically add salt. If the turkey was brined, injected, or heavily seasoned before cooking, there may already be plenty of salt in the carcass, and that salt becomes more concentrated as the stock reduces. Add salt at the end only if the finished stock actually needs it.

Remove the larger bones and vegetables with tongs or a slotted spoon, then carefully pour the remaining liquid through a fine mesh strainer into a clean container. Discard the bones, vegetables, and other solids once all of the stock has been strained.

Divide the hot stock into smaller, shallow containers so it can cool more quickly, or place the containers into an ice water bath and stir the stock occasionally to help bring the temperature down. Once cooled, cover the containers and place them in the refrigerator.

After the stock has chilled completely, the turkey fat will rise to the surface and become firm, making it easy to remove with a spoon. You can remove all of it or leave a little behind depending on how you plan to use the stock and how rich you want it to be.

Store the finished turkey stock in the refrigerator and use it within 3 to 4 days, or divide it into useful portions and freeze it for later.