Peel carrots and cut into large chunks. Cut potatoes into halves (and quarters for larger potatoes). Cut onions into chunks.
In a small mixing bowl combine garlic salt, black pepper, and half of the olive oil. Stir to combine.
Place oxtails into a large mixing bowl. Pour the olive oil mixture over the meat and using gloved hands, toss meat to coat.
Turn Instant Pot to the saute function and add remaining olive oil to the pot. Brown oxtails on both sides then remove to a plate.
To the Instant Pot, add onion and saute for 2-3 minutes until tender.
Add garlic, tomato paste, liquid smoke, soy sauce, balsamic vinegar, beef bouillon base, and water. Stir to combine then add oxtails back in, making sure they are submerged.TIP - We use a beef bouillon base and reconstitute it with water. If you prefer you can use 11/2 cups of beef broth or stock in place of the base and water.
Add carrots and potatoes.
Close lid and turn vent to closed position. Cook on high pressure for 40 minutes with a natural release.