Season the beef generously with kosher salt and black pepper.
Heat the canola oil in a large Dutch oven or heavy pot over high heat until it begins to shimmer.
Add the beef pieces in batches if needed, browning each side thoroughly for about 5 minutes per side; transfer browned beef to a plate.
Put the diced carrots, onion, celery, and chopped garlic into the pot; sauté while stirring and scraping the bottom to loosen browned bits, cooking until vegetables gain a light golden color, roughly 6 minutes.
Remove the vegetables to a heatproof bowl and set aside.
Pour the chicken stock into the pot and bring to a simmer, scraping any browned bits from the bottom for extra flavor.
Chop the browned beef into chunks and return them to the pot along with the reserved bones if using, plus the herb sachet.
Bring the mixture to a gentle simmer; lower the heat to maintain a very low simmer and cook uncovered until the beef turns tender, between 1 and 2 hours, skimming off any foam or impurities that surface.
Remove and discard the bones and herb sachet from the pot.
Add the pearled barley, previously cooked vegetables, and fish sauce if desired.
Let the stew continue to simmer gently for about 30 minutes until both the barley and vegetables have softened.
Taste and adjust seasoning with salt and pepper as needed.
If the stew appears too thick, add water a little at a time to reach your preferred consistency.
Serve the stew hot, sprinkled with minced fresh parsley for a bright finish.
