Set your Instant Pot to the Sauté setting. When display reads "hot", heat the butter/ghee and sauté the onions, celery, and carrots for 2 minutes, or until softened.
Add beef bone broth, tomatoes, bay leaves, thyme, rosemary, salt, and peppercorns and stir.
Add in the oxtails.
Using the Manual setting on the Instant Pot, adjust to high pressure and set to cook for 30 minutes. When time is up, allow pressure to naturally release.
Skim off any excess fat, remove the bay leaves and peppercorns and add the red wine vinegar.
If you wish to thicken the ragout, blend the arrowroot into 2 tablespoons of water. Bring the ragout to a boil on the Sauté setting and stir in the arrowroot mixture.
Boil gently, stirring constantly until the ragout has thickened, about 2 minutes. Serve and enjoy!