Peel and cut potatoes into the size of matchsticks. Keep slices in a bowl of water until ready to cook. Right before adding to wok, dry them off with a towel or paper towel.

Cut pork into slivers and combine with scallion slivers, soy sauce, sesame oil and cornstarch to marinate.

Heat wok until hot. Add 2 tablespoons peanut or canola oil and heat until first wisps of smoke appear. Add potatoes and stir-fry, flipping and tossing. Add rice wine vinegar and salt and continue stir-frying until potatoes are just cooked through, 2-3 minutes. They should still be somewhat crisp, not at all mushy. Remove from wok and set aside.

Wipe out wok and reheat until hot. Add 2 tablespoons peanut oil and heat until wispy. Add marinated pork and scallions to wok, letting sear a minute, then stir-frying until the pork is no longer pink. Add the leek and peppers and continue flipping and tossing until they are cooked through but still green and slightly crisp.

Add back potatoes and toss together briefly to meld the flavors. Sprinkle with ground Sichuan pepper if using. Check for salt and add some if needed. Check potatoes for doneness, but do not overcook. Remove and serve.