Fill a 5-to 7-quart pan with water and bring to a boil
Once water is boiling, blanch pork for 2 minutes. Remove pork and set to the side, then discard the water.
Rinse out the pan, then add vegetable oil and saute the shallots on medium heat.
Once shallots have begun to cook through, fill ⅔ of the pan with water and add the pork, fish sauce, mushroom seasoning, and salt. Bring to a boil.
Once the soup is boiling, add the carrots and beets and cook for 5 minutes, skimming occasionally. It's very important to regularly skim the surface of the soup so that the final product is clear and colorful.
After boiling for 5 minutes, add the potatoes and chayote squash and cook for an additional 15 minutes. Continue skimming.
After 15 minutes, taste the soup and add your desired amount of salt, pepper, and fish sauce.
Garnish with chopped Chinese celery and green onion, then serve hot with rice and bread. Enjoy!