Master stock varies from chef to chef, but is usually based on soy sauce, rice wine, rock sugar, fresh ginger and star anise. The nice thing about it is that it can be kept and used again and again, simply freshened up with some new spices.  When cooking duck, strain the stock and bring it back to the boil, then cool it and store it in the fridge or freezer. Remarkably, it matures with age. In Cantonese cooking, a whole chicken is cooked in the same way.
Click for a wonderful recipe for Shanghai soy duck with master stock