In a large bowl, add 1/2 teaspoon sea salt, 1/2 teaspoon MSG, 1/4 teaspoon white pepper, 1/4 teaspoon Chinese 5-spice and 1 teaspoon rice wine. Add 2 large skinless, boneless chicken breast fillets (diced) and mix well. Set aside for 5 minutes. Add 1 egg and mix once more. In a separate bowl, combine 5 tablespoons potato starch and 5 tablespoons custard powder.
Heat oil for deep frying to 180C. Working in batches, transfer some of the seasoned chicken into the bowl of potato starch and custard powder and mix well. Don't worry if the chicken pieces aren't completely coated in flour - the sticky coating will crisp up during cooking. Shake off any excess flour and carefully drop the coated chicken pieces into the hot oil. Fry for 3-4 minutes or until golden and crispy. Remove from the oil with a slotted spoon, drain off any excess oil and set aside on a plate.
At this stage Chinese takeaway style crispy chicken is ready to use as per your chosen recipe. Alternatively, set it aside to cool completely, cover and store in a food safe container in the fridge for up to 2 days or in the freezer for up to 3 months.