01 - Pat the beef cubes dry with paper towels and season generously with salt and pepper.
02 - In a large Dutch oven or heavy-bottomed pot, heat the oil over medium-high heat. Brown the beef in batches until well-seared on all sides. Transfer browned beef to a plate.
03 - Add onions, garlic, and celery to the pot. Cook for 3–4 minutes, stirring and scraping up browned bits from the bottom.
04 - Stir in tomato paste and flour, and cook for 1 minute to develop flavor.
05 - Return the beef to the pot. Pour in the Guinness (if using) and beef stock, stirring to combine and fully incorporate.
06 - Add carrots, parsnips, potatoes, bay leaves, thyme, and rosemary. Bring to a gentle simmer.
07 - Cover and cook on low heat for 2–2.5 hours, or until the beef is fork-tender and the vegetables are soft, stirring occasionally. Skim any excess fat from the surface if needed.
08 - Remove bay leaves. Taste and adjust seasoning with salt and pepper as needed.
09 - Serve hot, garnished with chopped parsley.