Preheat oven to 400 degrees.
Cut carrots and celery into 2-3 inch long pieces.
Toss bones, carrots, celery, and garlic with oil, salt, and pepper.
Place in roasting pan.
Roast for 45 minutes.
Remove from oven and pour into a large stockpot.
Add a little bit of water to the roasting pan.
Heat on a burner, stirring, until all the little bits of meat and vegetables come loose and it reduces down just a bit.
Pour into stockpot.
Add bay leaves, thyme, and water.
Bring to a boil and then reduce heat to a simmer.
Simmer until the stock reduces by nearly half, about 4 hours.
Pour into a lidded container, straining out solids.
Place in refrigerator overnight.
Remove from refrigerator and spoon fat from top of stock.
Use within a few days or portion and freeze.