Heat a large wok or frying pan.
Clean the chicken inside and out with damp kitchen roll.
Add the vegetable and peanut oil to the wok form. Add the brown sugar and heat over mild heat until the sugar caramelizes.
Mix in the soy sauce. Place the tenderloin in the wok and turn to the other side in the mixture so that it is thoroughly coated on all sides.
Add the water, garlic, onion and chili.
Cover and turn the chicken occasionally to the other side over low heat and steam until cooked through, about 1 hour. To check if it is done, pierce a chicken knuckle with the tip of a knife or a skewer. If clear liquid flows out, the meat is done.
Remove the chicken from the wok and set aside. Increase the temperature until the sauce in the wok thickens. Place the tenderloin on a serving plate, garnish with celery leaves and chives, and bring to the table along with the sauce.
5 Add a tbsp very finely chopped fresh ginger and 1 tbsp ground Szechuan pepper.
Our tip: Fresh chives are much more aromatic than dried ones!