Cut the beef into matchstick-sized pieces. Marinate with bò kho seasoning, minced garlic, 1 tablespoon oyster sauce, and 1 tablespoon soy sauce. Cover and let it marinate for 1 hour.

Sauté the smashed lemongrass until fragrant, then add the beef and stir-fry briefly. Add the coconut water and an equal amount of water, bring to a boil, then reduce heat and simmer for 30-45 minutes until the beef is tender. Add the daikon and carrot, and cook for another 10 minutes. Season to taste. If you prefer a thicker broth, add the cornstarch mixture.

Ladle into bowls and serve with baguette and fresh herbs. Add chili oil and hoisin sauce if desired.