Step 1

Cut a thin slice from base of each potato. Stand potatoes on flat bases and slice lengthwise into ⅛"-thick planks. Working with a few planks at a time, stack potatoes and slice into long ⅛"-thick matchsticks. (Alternatively, use a mandoline fitted with the julienne attachment.) Place in a large bowl and pour in cold water to cover; let soak 10 minutes. Swish potatoes around with your hands to release some starch, then drain well and pat dry.

Step 2

Heat oil in a large skillet or wok over medium-high. Cook chiles and Sichuan peppercorns, stirring constantly, until aromatic, about 1 minute. Add garlic and cook, stirring, until fragrant, about 20 seconds. Immediately add potatoes; cook, tossing constantly, until potatoes are wilted and crisp-tender but not browned, about 5 minutes. Remove from heat and stir in scallions, vinegar, and salt.

Step 3

Transfer stir-fry to a plate and top with cilantro. Serve with rice.