Prepare the pork marinade by mixing ½ tsp soy sauce, ¼ tsp white pepper, ¼ tsp salt, 1 tbsp water, and ½ tbsp cornstarch
Marinate the 5 oz pork loin in the mixture
Bring 4 cups of chicken broth and 2 cups of water to a boil
Add 4-5 slices of ginger to the broth
Add the marinated pork loin to the boiling broth
Add ½ oz of dried mushrooms to the soup
Add 1 lb of watercress to the soup
Simmer until all ingredients are cooked through
Serve hot