In a large bowl, toss the beef with flour, salt, and pepper until evenly coated.
Heat olive oil in a large Dutch oven or heavy-bottomed pot over medium-high heat. Brown the beef in batches, about 2-3 minutes per side. Remove beef from the pot and set aside.
Add the chopped onions to the pot and cook until softened, about 5-7 minutes. Add the minced garlic and tomato paste and cook for another minute until fragrant.
Pour in the Guinness stout and beef broth, scraping up any browned bits from the bottom of the pot.
Return the browned beef to the pot. Stir in the Worcestershire sauce.
Bring the stew to a simmer, then reduce the heat to low, cover, and cook for 1.5 hours, or until the beef is tender.
Add the carrots and potatoes to the pot. Cover and continue to cook for another 30-45 minutes, or until the vegetables are tender.
Taste and adjust seasoning if necessary. Serve hot, garnished with fresh parsley.
Notes
This stew is even better the next day as the flavors meld together.