1. In a large bowl, add all the ingredient A and mix well. Knead mixture with hands until it becomes smooth and elastic.
2. Shape meatball mixture into small balls. Heat up some cooking oil in a wok or pot on medium-high. When the oil is hot, place the meatballs into the frying pan gently. Fry them, turning till browned on all sides and cooked through. Set aside.
3. Make the bechamel sauce In a medium saucepan, heat the butter over medium-high heat until melted completely. Add the flour and stir them together until smooth. Reduce the heat to medium, and then pour the milk a little at a time, whisking constantly, until the mixture thickens and smoothens. Add sour cream, heavy cream (optional), soy sauce, salt, sugar and mix well. Remove from the heat.