01 - Pat the beef cubes dry with paper towels and season generously with salt and pepper.
02 - Heat 2 tbsp oil in a large Dutch oven or heavy pot over medium-high heat. Working in batches, brown the beef on all sides. Remove and set aside.
03 - Reduce heat to medium. Add remaining oil, onions, and celery. Sauté for 5 minutes until softened. Add garlic and cook for 1 minute more.
04 - Stir in the flour and tomato paste, cooking for 2 minutes to form a roux.
05 - Gradually pour in Guinness (if using) and scrape up any browned bits from the bottom.
06 - Return the beef to the pot. Add beef stock, carrots, potatoes, Worcestershire sauce, bay leaves, thyme, and rosemary. Stir well.
07 - Bring to a gentle boil, then reduce heat to low. Cover and simmer for 2 hours, stirring occasionally, until the beef is fork-tender and the gravy has thickened.
08 - Taste and adjust seasoning. Remove bay leaves.
09 - Garnish with fresh parsley and serve hot.