For the sauce, put the red pepper, chunks of chilli and pineapple juice in a pan and bring to the boil. Cover and cook for 10 mins, then sweet and sour sauce in a food processor. Return to the pan with the pineapple chunks, chilli halves, star anise, tamarind, sugar and vinegar. Gently simmer for 20-30 mins until reduced and sticky.
Keep warm, or reheat to serve. Fill a large pan 1cm deep with oil and heat until shimmering. Whisk the soda water and 100ml cold water into the self-raising flour with a little salt. Tip the cornflour onto a plate, line a tray with kitchen paper and turn on the oven to low. Dust the chicken with cornflour, then dip into the batter. Turn up the heat to keep the chicken frying, if needed, and cook for 5-6 mins, turning once. When cooked, drain on the tray, and keep warm in the oven.
