In a large Dutch oven or heavy pot, heat 1 tablespoon of vegetable oil over medium-high heat. Add the beef cubes in batches, searing until browned on all sides, about 5-7 minutes per batch. Remove and set aside.
Add tomato paste to the vegetables, cooking for 2 minutes. Sprinkle flour over the vegetables, stirring constantly for 2 minutes.
Return the beef to the pot and pour in beef broth, Guinness, and Worcestershire sauce. Add thyme, bay leaves, salt, and pepper. Stir and simmer for 1.5 to 2 hours.
Stir in diced potatoes, cover, and cook until potatoes are tender, about 20 minutes. Add peas and cook for another 5 minutes.
Serve hot, garnished with parsley and accompanied by crusty bread.
Notes
Store leftovers in an airtight container in the refrigerator for up to 3 days or freeze for 3 months. Reheat gently before serving.