Heat half the sunflower oil in a large pan and fry the meat cut into small cubes until browned. Remove meat and wipe the pan. Heat the remaining sunflower oil in the same pan and add the onions and garlic. When the onion is tender, add the ginger and lemon grass and cook until they become fragrant. Return the meat to the pan and add water, broth, sugar and coconut milk. Bring to a boil, reduce heat, cover with a lid and simmer for about 1 hour. Remove the lid and cook for another 45 minutes or until the meat becomes tender. Finally, add the lemon juice, fish sauce, coconut cream and coriander. Mix well and remove from heat. Serve with aromatic rice such as Jasmine.