In a small bowl, combine the black vinegar, sugar, light soy, Shaoxing wine, and dark soy. Stir in the cornstarch slurry until smooth and set aside — stir again right before pouring.

Place the raw peanuts in a dry pan over medium-low heat. Toast for about 5 minutes, tossing often, until lightly golden and fragrant. Remove and set aside.

Heat the oil in a wok over medium heat. Add the Sichuan peppercorns, then the dried chilies, and sauté for about 15 seconds until deeply fragrant — do not let them blacken.

Turn the heat to high. Add the king oyster mushrooms and stir-fry for 1 minute to sear the edges. Add the garlic, ginger, and leek; cook 1–2 minutes more until tender but still bouncy.

Give the sauce one last stir and pour it in. Keep stirring until it thickens and coats everything in a shiny, clingy glaze.

Add the toasted peanuts last, toss quickly to combine, and serve immediately with steamed rice.