Prepare the sauce: In a small bowl, whisk together the light soy sauce, dark soy sauce, black vinegar, tomato purée, sugar, cornflour, and chicken stock. Set the bowl aside; you'll notice the mixture is a deep, rich brown colour with the aroma of tangy vinegar and sweet tomato.

Marinate the chicken: Place the chicken thigh chunks in a mixing bowl and add 1 tablespoon of the prepared sauce. Toss everything together until each piece is evenly coated. The chicken will look glossy and smell faintly of soy. Leave it to sit while you prepare the aromatics.

Toast the peppercorns: Place a large frying pan or skillet over a medium heat. Add the Sichuan peppercorns and dry-fry them for about 30 seconds, shaking the pan occasionally. You'll know they're ready when you hear a faint crackle and a warm, citrusy, numbing aroma fills the air. Tip them out onto a plate and roughly crush them with the back of a spoon.

Fry the chillies and aromatics: Return the pan to a high heat and add the vegetable oil. When the oil shimmers and you see faint wisps of smoke, add the dried red chillies and the crushed Sichuan peppercorns. Stir-fry for 20 seconds until the chillies darken slightly and release a smoky, pungent smell. Immediately add the sliced garlic and grated ginger. Stir for another 30 seconds, until the garlic turns a pale gold and smells fragrant.

Cook the chicken: Add the marinated chicken chunks to the pan in a single layer. Let them sear undisturbed for 2 minutes — you're looking for a deep golden-brown crust on the underside. The sizzling sound will be lively and sharp. Flip each piece and cook for another 2 minutes, until the chicken feels firm to the touch and is lightly charred in spots.

Add the sauce and spring onions: Pour the reserved sauce mixture into the pan. It will immediately bubble and steam, thickening into a glossy, dark lacquer. Stir the chicken to coat it evenly. Add the spring onion lengths and the roasted peanuts. Toss everything together for about 1 minute, until the spring onions have softened slightly but still retain a vibrant green colour and a slight crunch.

Serve immediately: Spoon the Kung Pao Chicken over a bed of steamed jasmine rice. The sauce should be thick enough to cling to each piece of chicken and nut, with a sticky, almost caramelised finish. Garnish with extra sliced spring onions if you like.