Parboil oxtails for approximately 30 minutes. Rinse under warm water four times and trim of any excess fat.
Return oxtails to stock pot, adding dried orange peel, star anise, and ginger. Reconstituted shitake mushrooms can also be added at this time as an option. Add water so that it's about 2" above the oxtails. Bring to a rolling boil and reduce heat to simmer. Add salt to taste. We normally would use rock salt but coarse sea salt or kosher salt will work. I prefer to undersalt and adjust seasoning at the end.
Simmer for approximately 1 hour, skim any foam/scum that may appear on the surface. Add peanuts.
Simmer for an additional 2-3 hours or until oxtails are tender. Set aside to cool, then refrigerate overnight.
Remove from refrigerator and remove any remaining scum and congealed fat.
To serve, reheat for about 30 minutes on low, or until warmed through. As an option slice 2 heads of Kai choy cabbage into 2 inch pieces, parboil and drain. Add to soup as it is reheating. Place 3-4 oxtails in each bowl, with enough broth to cover. Garnish with chopped cilantro, chopped green onions,freshly grated ginger and soy sauce.
Serve with steamed rice in a separate bowl and hot tea.
Mandarin orange peel are sold in Chinese medicinal shops as chen pi. Orange peel is sold by McCormack on the spice rack (2 tsps). You can make your own. Wash and peel an orange by taking off the peel in wide strips with as little of the pith as possible, or remove the whole skin off a mandarin. Place peel in a single layer spread on parchment paper in the oven at 200 degrees F. for about25-25 or until it is crispy. and curled, times may vary so make sure it does not burn, turn halfway through.