Pat shrimp very dry. Marinate in fish sauce for 10–15 minutes. Drain off excess.

Lightly toast peppercorns and salt in a dry pan over medium heat until fragrant, then grind coarsely. Mix in white pepper.

In a bowl, toss shrimp with cornstarch and half of the toasted pepper‑salt mixture. Heat oil in a wok/skillet to around 350 °F (175 °C). Fry shrimp in batches for ~1 minute per side until golden and crispy. Transfer to paper towel–lined rack.

After first fry, increase oil temp to ~375 °F and fry shrimp again quickly for extra crunch. Drain again on paper towels.

Discard most oil, leaving about 1 Tbsp in wok. Sauté garlic & ginger over low heat ~2 minutes until aromatic. Add chilies and scallion whites and stir 1 minute.

Turn heat high; return shrimp, toss briefly to combine with aromatics. Off heat, stir in scallion greens, remaining spice mix, and cilantro. Taste and add salt if needed. Serve immediately.