Sprinkle the beef generously with salt and pepper. Heat canola oil in a large Dutch oven or pot over high heat until just smoking. Brown the beef pieces evenly, working in batches to avoid crowding, about 5 minutes per side. Remove browned beef and set aside.
Add the diced carrots onion celery and garlic to the pot. Cook stirring often and scraping any browned bits until the vegetables start to caramelize and soften about 6 minutes. Transfer these vegetables to a bowl.
Pour the chicken stock into the pot and bring it back to a simmer while scraping along the bottom to lift up any flavorful browned bits.
Cut the browned beef into smaller chunks then add the beef the reserved bones if using and the sachet of thyme bay leaf and peppercorns into the pot. Maintain a gentle simmer and cook uncovered until the beef becomes tender usually between 1 and 2 hours. Remove any foam from the surface during cooking.
Once the meat is tender remove and discard the bones and herb sachet. Stir in the pearled barley the reserved cooked vegetables and the fish sauce if using. Continue simmering until the barley and vegetables are soft but still hold their shape roughly 30 minutes.
Taste and adjust seasoning with salt and pepper. If the stew is thicker than you'd like add a bit of water to reach your preferred consistency. Serve the stew hot garnished with fresh minced parsley.