Gunpowder chicken with dried red chillies peanuts

Name: Gunpowder chicken with dried red chillies & peanuts
Ingredients: 12 boneless, skinless chicken thighs (about 900g), cut into pieces; 1 tbsp dark soy sauce; 2 tbsp vegetable oil; 15 whole dried bird's-eye chillies; 1 tsp Sichuan peppercorn, ground; bunch spring onions, cut into 2.5cm pieces; 50g whole roasted peanut; 5 tbsp dark soy sauce; 2 tbsp Shaohsing rice wine; 4 tbsp Chinese black vinegar; 4 tbsp chicken stock; 1 tbsp caster sugar; 1 tbsp cornflour, mixed into 1 tbsp water