Add olive oil to the InstantPot and set to ‘Saute”.
In a shallow medium-sized bowl, combine flour, ½ teaspoon salt and ½ teaspoon pepper. Add beef, tossing to evenly coat in flour. When the oil is shimmering, add beef and cook for about 2-3 minutes on each side, or until brown. Remove from the pot with a slotted spoon and set aside.
Add onion, garlic, carrots and celery to the pot along with the remaining ½ teaspoon salt and ½ teaspoon pepper. Cook, stirring often, until the vegetables begin to soften, about 5 to 7 minutes.
Add the thyme, tomato paste and Worcestershire sauce and stir to coat the vegetables. Cook for 1 minute. Add the beef stock, scraping the bottom of the pan to loosen any brown bits that have formed. Add the sun-dried tomatoes, baby potatoes, and reserved beef to the pot.
Cook at manual high pressure for 30 minutes, then let the pressure release naturally for 15 minutes. Release the remaining pressure manually, then return the pot to the “Sauté” function. Remove about ¼ cup of the cooking liquid and set in a small bowl. Add cornstarch and whisk until smooth and combined. Once the stew reaches a boil, add the cornstarch mixture back in and cook for about 2 minutes, or until thickened.
Add the peas and cook for another 2 minutes, or until bright green and tender. Hit ‘cancel’ on the InstantPot to stop the cooking, let cool slightly, then serve.