1. Heat 1 tablespoon oil in a wok over a medium high heat. Put in the onions, garlic, and whole green onions and stir-fry for 2 minutes. Add the lemon grass and continue to stir until the onions become lightly brown, remove the green onions and set aside.
2. Heat the remaining oil over a high heat. Stir-fry as many pieces of beef as are convenient until they are brown, turning them over from time to time. Continue until all the beef has been cooked.
3. Add the water. Add the lemon grass mixture, yellow bean sauce, chili powder, star anise, cinnamon, peppercorn, and sugar, and bring to a boil. Cover and lower the heat to simmer gently for 1 hour.
4. Add the reserved green onions; cover again and allow to simmer for a further 15 minutes or until the sauce has thickened a little and the meat is tender.