Mix together the egg white, cornflour, half the sea salt and the cod, and leave for 10 minutes.
Heat a wok until almost smoking. Add the vegetable oil and, when hot, remove the fish from the marinade and stir-fry in batches until golden brown, then remove from the wok. Reheat the wok and stir-fry the carrot, spring onions, ginger and garlic until fragrant. Deglaze the wok with shaoxing, then add the snow peas, stock, sesame oil, remaining sea salt and white pepper and stir-fry for 1 minute more. Return the cod to the wok and toss together before serving.