Begin by seasoning the beef with salt and pepper. In a large pot or Dutch oven, heat the canola oil on high until it shimmers. Sear the beef pieces, ensuring they are browned on all sides, about 5 minutes per side, and set them aside on a plate once cooked.

Add the diced carrots, onion, celery, and garlic to the same pot. Stir thoroughly while scraping the bottom to release any browned bits, and cook for around 6 minutes until the vegetables are slightly caramelized. Move to a heatproof bowl and set aside.

Pour in the chicken stock, returning the heat to medium and scraping any stuck bits. Cut beef into smaller pieces and add back to the pot with any reserved bones and the herb sachet. Allow it to reach a gentle simmer.

Reduce the heat and let it simmer for 1 to 2 hours, or until the beef is tender. Remember to skim off any foam that may form on the surface.

After cooking, discard the bones and the herb sachet from the pot. Incorporate the barley, reserved vegetables, and the fish sauce if using. Let it simmer for around 30 minutes until the barley is tender.

Taste the soup and adjust seasoning with additional salt and pepper as needed. If the consistency is too thick, add a little water. Serve the soup hot, topped with fresh parsley.