Brown the Beef
Set the Instant Pot to the sauté function and add olive oil.
Season beef cubes with salt, pepper, and Italian seasoning.
Add beef to the pot in batches and brown on all sides (about 2–3 minutes per batch). Remove and set aside.
Sauté Aromatics
Add chopped onion and garlic to the pot. Sauté for 2–3 minutes until softened.
Pour in a splash of beef broth and scrape up any browned bits from the bottom with a wooden spoon (this prevents the burn warning).
Add Remaining Ingredients
Return the beef to the pot. Add carrots, potatoes, celery (if using), Worcestershire sauce, tomato paste or sauce, and the rest of the beef broth. Stir to combine.
Do not add cornstarch or peas yet.
Pressure Cook
Lock the lid and set the steam valve to “sealing.”
Cook on high pressure for 35 minutes.
Allow the pressure to release naturally for 10 minutes, then do a quick release for any remaining pressure.
Thicken the Stew
Mix cornstarch with cold water in a small bowl to make a slurry.
Turn the Instant Pot to sauté mode. Stir the slurry into the stew and simmer for 2–3 minutes until thickened.
Stir in peas, if using, and cook for 1–2 minutes until heated through.
Serve
Taste and adjust seasoning as needed.
Ladle into bowls and garnish with chopped parsley.
Serve hot with crusty bread or a green salad for a complete meal.