Combine all the marinade ingredients, except the cornflour and oil, with 1/4 tsp salt in a large bowl, then stir in the chicken thigh pieces to coat. Cover and chill for 30 mins. Add the cornflour and mix well, then add the oil and stir again to combine.

Put the dried Sichuan chillies in a colander and shake to remove any excess seeds. Transfer to a heatproof bowl, cover with hot water and leave to soak for 10 mins, then drain and set aside.

Fill a wok or large saucepan about a third full with the oil and heat over a medium-high heat until the oil forms bubbles around a chopstick when it's dipped in (this is about 160C). Reduce the heat to medium and carefully lower in the chicken thigh pieces. (You may need to do this in batches.) Fry for 3-4 mins, then remove to kitchen paper to drain using tongs. Turn the heat up until the oil reaches between 180C-200C, and fry the chicken for a further 1-2 mins until golden, crispy and cooked through. Drain on kitchen paper. (You may need to do this in batches.)

Drizzle a little oil into a wok over a medium heat and stir-fry the red and green peppercorns, rehydrated Sichuan chillies, the ginger, garlic and white parts of the spring onion for about 2-3 mins. Add the chicken, roasted peanuts and green parts of the spring onion, and cook for a further 3 mins. Scatter in the sesame seeds, then add the soy sauce and sugar. Stir well, then serve.