For the Mushrooms:
Trim off and discard the root end of the mushrooms and pull them all apart as much as you can. Combine the three types of mushrooms in a bowl. Do not wash them.
For the Szechuan Spiced Salt: To make the spiced salt, put the chiles and Szechuan peppercorns in a dry wok. Toast the spices over low heat, tossing them around to make sure not to burn them. When you start to smell the fragrance from the spices, after about 3 minutes, turn off the heat. Transfer the spices to a plate to cool. Pulse the cooled spices a few times in a blender or mini food processor until they are pulverized. They don't have to be ground into a fine powder. Combine with the coarse sea salt in a bowl and mix well.
For the Batter: To make the batter, combine the cake flour, tapioca starch, and salt in a bowl and mix well. In a separate bowl, whip the egg white until it holds soft peaks. Whisk 1-1/2 cups ice-cold water into the flour mixture. Don't worry if the resulting batter is a little lumpy. Fold in the egg white.
Heat the vegetable and sesame oils together in a wok to about 350 degrees F, or to the point when a drop of the batter sizzles and rolls in the oil. Separate the mushrooms into four equal batches. Put one portion in a small bowl and ladle about one-quarter of the batter over it. Coat the mushrooms evenly in the batter and then drop them into the hot oil. Fry the mushrooms for about 3 minutes and then turn them over. Continue to fry for another minute, until crisp and creamy in color but not browned. Using a skimmer, transfer the mushrooms to a paper towel to drain. Immediately start to fry the next batch.
Work as quickly as possible so you can serve the mushrooms hot.
Sprinkle chopped scallions and cilantro over the mushrooms and serve with the spiced salt alongside.
Recipes and images reprinted from Phoenix Claws and Jade Trees: Essential Techniques of Authentic Chinese Cooking. Copyright © 2015 by Kian Lam Kho.