Place the chicken carcass in a large pot or slow cooker.
Add the carrots, celery, onion, garlic, bay leaf, and thyme.
Fill the pot with water until the carcass and vegetables are fully submerged.
Bring the mixture to a boil over high heat, then reduce the heat to low and let it simmer. If you’re using a slow cooker, you can set it to low and let it cook for 8-10 hours.
Periodically skim off any foam or fat that rises to the surface.
After the broth has simmered, strain it through a fine-mesh sieve into a large bowl or another pot, discarding the solids.
Season the broth with salt and pepper to taste.
Let the broth cool, then store it in the fridge or freezer until you’re ready to use it.