For the chicken, place the egg into a bowl, add the cornflour and a pinch of salt and whisk well to combine. Add the chicken to the mixture and coat well in the egg.
Heat a wok until smoking and add the groundnut oil. Fry the chicken for 4-5 minutes, or until golden-brown and crisp, then remove with a slotted spoon and drain on absorbent kitchen paper.
For the stir fry, pour off all the oil from the wok, except for one tablespoon. Reheat the oil over a high heat, add the onion and stir fry for a few seconds. Add the yellow and red pepper slices and stir fry for one minute, or until softened. Add the chicken pieces and stir fry for 1-2 minutes, then add the stock and soy sauce. Simmer for another minute, or until the chicken is cooked through.
Stir in the spring onions and cashew nuts, season, to taste, with sea salt and ground white pepper and transfer to a serving dish. Serve immediately with steamed rice.