1. In a cooking pot, heat 1 tsp vegetable oil and cook the pork. When the pork is almost cooked, add carrot, leek and shiitake. Stir-fry for a few minutes.
2. Pour the water (800ml) and bring it to a boil, adding chicken soup powder, cooking sake, soy sauce, kosher salt, oyster sauce.
3. Once it has boiled then add tofu and bring it to a boil again. Add vinegar (1 or 2 tbsp, depending on your taste). Pour the dissolved potato starch to thicken the soup. Then add the beaten eggs but don't mix them in until the eggs are cooked.