Set the instant pot to sauté mode and melt 2 tablespoons of butter. Pat the beef dry with paper towels, season with salt and black pepper, and sear on both sides until golden brown. Remove and set aside.

Add the sliced onions to the pot and cook on medium heat until soft and caramelized. Deglaze with red wine vinegar, scraping up browned bits from the bottom of the pot.

Pour in the beef broth, then return the roast to the pot. Add the potatoes, garlic, thyme, salt, black pepper, and bay leaf.

Secure the lid and set the instant pot to manual high pressure. Cook for 20 minutes per pound, about 60 minutes for a 3-pound roast. Let the pressure naturally release for 20 minutes before opening.

Remove the bay leaf. Shred or slice the beef, then serve with potatoes. Use the broth as a savory sauce or create an onion gravy by mixing a cornstarch slurry in a small bowl and stirring it into the pot.

Store leftovers in an airtight container in the fridge for up to four days or freeze in a freezer-safe container for up to three months.