Cut the meat into 1-inch cubes. Place in a large mixing bowl. In a small mixing bowl, combine the fish sauce, water, cornstarch, sugar, baking powder and sesame oil
. Season with black pepper. Whisk
well and add the beef. Toss well. Cover and refrigerate overnight. Remove from the refrigerator and place in the bowl of a food processor
, fitted with a metal blade. Process until smooth. To test, bring a small pot of water to a boil, add a teaspoon of the mixture to the water and cook for about 1 minute. Remove from the water, taste and adjust seasoning. Roll the rest of the mixture into individual balls, about 1 tablespoon for each ball. In a saucepan
, bring the beef stock to a boil. Add the meat balls, stirring occasionally. When the meat balls start to float
, cook for an additional 5 minutes. Stir in the green onions, Nuoc Cham and black pepper. Ladle into individual bowls and serve.