Set Instant Pot to Saute mode and add one tablespoon of olive oil.
Once oil is heated, add beef stew meat in a single layer on the bottom of the pot. You may need to do a few batches. Brown the beef on all sides. Once beef is browned, remove from pot and set aside.
Once all the beef is browned, add the second tablespoon of olive oil. Once that oil is heated, add onion, garlic, and celery.
Saute until the vegetables are tender. Remove from pot and set aside.
Add beef stock, tomato paste, and Worcestershire sauce to the pot and whisk until combined. Using a wooden spoon, scrape up all burned bits from the bottom of the pot.
Add meat and vegetables back into the pot. Add bay leaf, thyme, salt, and pepper. Stir to combine.
Add potatoes and carrots to pot - DO NOT STIR.
Put the lid on the Instant Pot and make sure it is set to 'sealing'. Set Instant Pot to Manual and cook on high pressure for 35 minutes.
When the timer goes off, let the Instant Pot naturally release for 20 minutes. Then do a quick release and remove the lid. Remove bay leaf.
Set Instant Pot to Saute mode. Mix together water and cornstarch. Pour into stew and stir gently. Be careful not to break up the vegetables.
As soon as the stew has thickened, serve immediately.