Mix together the prawns, rice wine, egg white and cornflour in a bowl until well combined.
Stir together all the ingredients for the sauce in a small bowl until smooth and set aside.
Heat the oil in a large nonstick wok or frying pan over a high heat until almost smoking. Add the prawns and stir-fry for 3–5 minutes until just turning pink, then remove with a slotted spoon to a plate.
Add the chillies and crushed Szechuan peppercorns to the pan and stir-fry over a high heat for 1–2 minutes until fragrant. Add the ginger, garlic and spring onions and stir-fry for about 30–40 seconds.
Return the prawns with their juices to the pan and toss to mix. Add the stock and bring to the boil. Stir in the sauce mixture and cook, stirring constantly, until it has thickened. Finally, add the cashew nuts, stir to mix well and serve immediately.