Freeze the pork tenderloin until firm, about 30 minutes; slice it into very thin slices, then into narrow strips. Refrigerate the pork. Put the tree ear mushrooms in a small bowl and the shiitake in another. Bring a small pot of water to a boil. Pour the hot water over the mushrooms and set them aside to re-hydrate for about 30 minutes.
Meanwhile, combine the broth, garlic, ginger, in a large sauce pan. Crush the white part of 1 scallion with the side of a knife, add to the pan, simmer, covered for 15 minutes.
Thinly slice the remaining scallions and reserve. Remove the mushrooms from the water and discard the liquid. Squeeze out any excess moisture from the shiitake and thinly slice.
Remove the garlic, ginger, and scallion from the broth and discard. Add the mushrooms, soy, vinegar, pepper, and salt and bring to a simmer. Whisk in the cornstarch mixture, bring to a boil, and then simmer over medium heat for 5 minutes. Pour the egg into the soup and stir once to make delicate threads. Stir in the remaining scallions, oil, tofu, and pork, return to a simmer. Remove from the heat to prevent the meat from getting tough, adjust seasonings to taste. Serve immediately.
From Food Network Kitchens