MAKE THE SAUCE: Whisk together all the sauce ingredients in a small bowl until smooth and blended.

MAKE THE STIR-FRY: In a large bowl, toss the mushroom cubes with the soy sauce, salt, and sesame oil, then let them rest for 5 minutes to release their liquid. Heat the vegetable oil in a wok over medium-high heat to 360°F (185°C), or until a wooden chopstick forms a merry stream of bubbles when inserted. While the oil is heating, check on the mushroom cubes—they should be damp. Add ½ cup of the starch to the bowl and squeeze the mushroom cubes to allow the starch to be absorbed. The mushroom cubes should still be slightly damp. Add the remaining starch and toss again, until each cube is coated with a generous amount. This will prevent them from sticking to each other when frying.

Fry the mushroom cubes in batches. Separate the cubes with your fingers as you drop them in to prevent them from clumping up. After about 15 seconds in the oil, the mushrooms will begin to sizzle and splatter as their internal water comes out. Stand back and wait until the splattering slows, then stir the cubes with a skimmer or spider until they are golden brown and crisp, about 2 minutes. Remove the cubes and transfer to a paper towel–lined dish. Bring the oil back up to temperature and repeat with the remaining mushrooms. Pour the oil into a heatproof container for another use, reserving 2 teaspoons in the wok.

Return the wok to medium heat. Stir-fry the ginger and garlic until fragrant, about 30 seconds. Add the dried chiles and peppercorns and stir-fry until the chiles start to darken, about 30 seconds. (Make sure your kitchen is well ventilated, as this will give off a stinging smoke.) Add the scallions, chile, and mushroom cubes, then increase the heat to high and pour the sauce down the side of the wok, so that it sizzles on the way to the bottom. Toss for 30 seconds, just until the sauce coats the mushroom cubes and everything is piping hot. Stir in the peanuts, remove from the heat, and serve