Preheat air-fryer at 200°C for a few minutes while preparing the chicken.
In a bowl, Beat the egg and add the chicken. Stir to coat the chicken pieces well.
In a second bowl, combine 5 tbsp cornflour with the baking powder and season with salt and pepper.
Toss the chicken pieces in the flour and stir to ensure the chicken are well coated.
Transfer the chicken pieces to the air-fryer basket and place in preheated the air fryer.
Cook for 12 to 18 minutes, giving a shake midway to ensure the chicken pieces are cooked through and coloured all around. You might need to cook the chicken in batches, depending on the size of the air fryer.
In the meantime, in a wok or sauté pan, over medium heat, heat some oil and add the chopped ginger, garlic and chilli. Cook for 15-20 seconds until just fragrant. Then pour the soy sauce, sweet chilli sauce, sake and rice vinegar and stock; Stirring to combine the flavours. Bring to the boil and simmer for a minute or so.
Next, in a small bowl, combine the last tablespoon of cornflour with enough cold water. Stir enough in the boiling soy mixture and simmer until the mixture reach a spoon coating consistency. Turn off the heat and check the seasoning.
Once the chicken are cooked, add the crispy chicken pieces to the soy mixture and toss to coat the sauce on the chicken.
Sprinkle some spring onion and sesame seeds.
Serve immediately with some boiled rice.