Add bones to the electric pressure cooker with 3 quarts of water. Add the vinegar. Using the saute function, bring the broth to a simmer. Using a slotted spoon, skim off any white or gray foam that develops on top.
Cover and lock the lid on the pressure cooker, making sure the pressure relief valve is closed. Set to manual, high pressure for 120 minutes.
When the 120 minutes is up, let the pressure naturally release for 90 minutes. Do not release the steam, let it come down from pressure on it's own.
After the 90 minutes, open the lid, and add the carrot and onion. Close the lid, and be sure the pressure relief valve is closed. Set to manual, high pressure for 120 minutes.
Natural release for 90 minutes when the second 120 minutes is up.
When the 90 minutes is up, strain and cool the bone broth as quickly as possible. Set a strainer over a large pot or a large stainless steel bowl like a stand mixer bowl. Carefully strain the bone broth into it. Discard the spent bits of bone and vegetables.
Prepare an ice bath by either filling a sink or basin with cold water and ice. Set the pot of broth inside the ice bath. Stir regularly until the broth is cooled to about 50°F, or for about 15 minutes. Transfer the broth to airtight containers or jars. Refrigerate or freeze.
