Step 1 Place the turkey carcass, meatiest side down, in a large stockpot. Fill the pot halfway with water. Bring to a boil and skim any scum off the surface. Reduce the heat and simmer 30 minutes. Remove the carcass to a carving board; let it sit until cool enough to handle.
Step 2 Add the onion, carrots, celery, parsley, peppercorns and bay leaf to the water in the stockpot and continue simmering.
Step 3Shred or cut any remaining meat off the carcass and set it aside in a bowl; cover and refrigerate.
Step 4Return the bones to the stockpot and continue simmering, adding just enough water every hour to cover. Cook until the stock is rich and aromatic, at least 3 hours or up to 6.
Step 5Cool, then strain, discarding solids. (If you have time, refrigerate the stock until it's well-chilled, then lift off the fatty top layer and discard.)