01 - Heat vegetable oil in a large Dutch oven over medium-high heat. Season beef cubes generously with salt and pepper. Brown beef in batches, turning to sear all sides evenly. Transfer browned meat to a plate and set aside.
02 - Add onion, carrots, parsnips, celery, and garlic to the same pot. Sauté for 5 minutes until vegetables begin to soften and release moisture, scraping up any browned bits from the bottom.
03 - Stir in tomato paste and cook for 1 minute to develop depth. Return browned beef to the pot, along with any accumulated juices.
04 - Pour in beef broth and stout if using. Add Worcestershire sauce, bay leaves, thyme, and rosemary. Stir thoroughly to incorporate all ingredients.
05 - Bring mixture to a boil, then reduce heat to low. Cover and simmer for 1 hour to begin tenderizing the beef and developing flavors.
06 - Stir in potatoes and barley. Cover again and continue cooking for 45-60 minutes, or until beef is fork-tender, barley is cooked through, and stew has thickened naturally.
07 - Remove and discard bay leaves. Taste stew and adjust seasoning with additional salt and pepper as needed to balance flavors.
08 - Ladle hot stew into serving bowls. Garnish with chopped parsley if desired. Serve immediately with crusty bread for soaking up the rich broth.