Make sauce: Mix sugar, soy sauce, and cornstarch. Set aside.
Season chicken: Pat dry the chicken. Season with a pinch of pepper and a pinch of salt.
Brown chicken: Heat the oil in a wok (see notes) over very high heat.Add the chicken and cook and stir constantly until it turns golden brown.
Add vegetables: Stir in the celery, peas and ginger, cook and stir for 30 seconds.Add the carrot, broccoli, and garlic, cook and stir for 30 seconds.Add the bell pepper, pak choi, baby corn, and leek, cook stirring for 30 seconds.
Add sauce: Add the soy sauce mix and cook stirring for 30 seconds, or until the sauce has thickened a bit.
Serve: Remove from the heat and serve immediately accompanied with arroz blanco.
Notes
For proper stir-frying, you need a seasoned wok and a high-flame burner. If you don't have either, the next best thing is to use a flat-bottomed cast-iron frying pan at the highest temperature your stovetop reaches.The secret ingredient in Chinese restaurants is MSG, available under the name brand Aji-no-moto (and others). Add a pinch to the sauce, or more to taste. Be mindful that the sodium content will be higher if this is something you worry about.No two Chop Suey recipes are alike. Other ingredients that can be used are mushrooms, broad beans, bamboo hearts, etc. Adapt the recipe to your taste.If you want to make a vegetarian version, eliminate the chicken and the corresponding steps. The trick to Chop Suey (cooked but crispy vegetables) is in short cooking at high temperature, the vegetables are added starting with the ones that take longer to cook to the ones that take less time.