Rinse off the oxtail pieces, pour them into plenty of boiling water and cook for 3 minutes. Strain with a coarse sieve and rinse. Wash the leek and cut into small pieces. Cut the washed and peeled ginger crosswise into thin slices.
Heat the water, dissolve the chicken stock and chicken stock powder in it. Heat a wok, add the oil and sugar. Melt the sugar over moderate heat. As soon as it is caramel colored, deglaze with 50 g of the chicken stock and stir until the sugar is completely dissolved. Add pieces of oxtail, leek and ginger. Baste chicken stock enough to cover the pieces. Simmer with the lid on for 90 minutes. Pour in some chicken broth if necessary.
In the meantime, separate the egg whites from the eggs, mix with 1 tablespoon of the chicken stock and a little salt and white pepper and pour into Chinese porcelain spoons. Place a parsley leaf on each of the egg mass. Carefully place the spoons in a steamer insert and steam over hot water. The development of steam should be moderate. Using a teaspoon, carefully peel off the whipped egg whites in the hot water from the edge of the porcelain spoon.
Wash the lettuce and line a serving dish with it. Place the egg white flowers on the edge. Strain the oxtail pieces, keep the stock. Detach the meat from the bones and place in the center of the serving bowl. Remove approx. 250 g of the broth and, together with half of the rice wine, reduce to half in a pan. Dissolve the tapioca flour and the soy sauce in the rest of the rice wine and bring to the boil briefly. Season the sauce with salt and pepper.
Drizzle the sauce over the oxtail pieces, finish garnishing, serve with rice and enjoy.