Place bones, stew meat (if using), onions, and carrots in a roasting pan; rum everything with a little olive oil.
Roast about 45 minutes, flipping bones, meat, and vegetables halfway through.
Bones should be browned, not charred (if they look like they are beginning to burn, turn heat down).
Remove everything and place in a large stockpot.
Place roasting pan over two burners, add about a cup of hot water and scrape browned bits from bottom of pan.
Pour into stockpot, then add enough water to cover bones by 2 to 3 inches; add celery, garlic, parsley, bay leaf, and peppercorns.
Heat stock to a low simmer (covered), then reduce heat and almost simmer (covered) for at least 3 hours, 6-8 is better; do not stir as this will combine the fat with the stock and cause it to become cloudy.
During cooking you can skim off any fat and scum from the top (the fat will solidify and can be used for cooking!).
Use tongs to remove bones and vegetables.
Strain stock through cheesecloth to remove all solids; let cool to room temperature.
Store in the refrigerator with the fat layer intact (it protects the stock from bacteria).
Remove fat if storing in the freezer; remember to leave an inch of headspace so your container does not burst in the freezer since it will expand.