1In a pot, combine beef shank, fish sauce, and water. Bring to a boil, then simmer for 1 hour or until beef is tender.
2Add batwan fruit juice and banana blossoms. Simmer for another 20 minutes.
3Season with more fish sauce if needed. Serve hot with steamed rice.
Batwan fruit provides a unique sourness to Kansi; if unavailable, you can use tamarind as a substitute. Adjust the sourness to your preference by adding more or less fruit juice.