Bring water and turkey carcass to a boil in a large pot.
Add 1 1/2 cup
chopped onion, 3 stalks celery, 1/2 cup chopped carrot, peppercorns, 1 pinch
thyme, and 1 bay leaf.
Simmer, skimming excess fat and foam from top of stock
as needed, 2 to 2 1/2 hours. Add more water to stock as it evaporates.
Remove carcass from stock and cool. Pull meat from bones and shred; refrigerate until
needed.
Strain stock and return liquid to pot.
Mix 1 1/2 pounds carrots, 2 onions, 6 stalks celery, barley, mushrooms,
2 bay leaves, salt, marjoram, black pepper, and 1 pinch thyme into turkey stock
and bring to a boil.
Reduce heat and simmer soup, stirring occasionally, until
barley is fully cooked, 1 hour and 20 minutes.
Add turkey meat to the soup and
simmer for 10 more minutes. Remove bay leaves before serving.