01 - Pat the beef cubes completely dry with paper towels. Season generously with salt and freshly ground black pepper on all sides.
02 - Heat vegetable oil in a large Dutch oven over medium-high heat. Sear the beef in batches, being careful not to overcrowd the pot. Brown on all sides, about 3-4 minutes per batch. Transfer browned beef to a plate and set aside.
03 - Add chopped onions and sliced celery to the same pot. Sauté for 4-5 minutes until softened and fragrant. Add minced garlic and cook for 1 additional minute until fragrant, being careful not to burn.
04 - Stir in the flour and tomato paste. Cook for 2 minutes, stirring constantly to coat the vegetables and cook out the raw flour taste. The mixture will become thick and fragrant.
05 - Pour in the Irish stout, scraping up any browned bits from the bottom of the pot with a wooden spoon. Let it bubble for 1-2 minutes to reduce slightly.
06 - Return the browned beef and any accumulated juices to the pot. Add beef stock, Worcestershire sauce, bay leaves, dried thyme, and dried rosemary. Stir everything together to combine.
07 - Bring the mixture to a simmer, then reduce heat to low. Cover tightly with the lid and cook for 1 hour, stirring occasionally to prevent sticking.
08 - Add sliced carrots, potato chunks, and sliced parsnips to the pot. Stir well to submerge vegetables in the liquid. Cover and return to a gentle simmer.
09 - Continue simmering covered for another hour, or until the beef is fork-tender and the vegetables are cooked through. The gravy should be thick and rich.
10 - Remove and discard the bay leaves. Taste the stew and adjust seasoning with additional salt and pepper if needed. Ladle hot stew into bowls and garnish with fresh chopped parsley.