Cut the chicken into pieces. Combine buttermilk with ½ tsp salt and add the chicken. Let marinate in the fridge for at least 1h, better overnight.
Combine flour, cornstarch, baking powder, ½ tsp salt and ½ tsp pepper. Toss chicken pieces, a few each time (allow them to drip off any excess), in the flour mixture to coat. Heat up oil to 160°C and fry your chicken until golden brown, ~4-5min.
Combine all ingredients of the sauce. Add to a (non-stick) pan and bring to heat. Add your chicken and toss until the sauce fully coats the chicken.
Cook the rice.
Prepare your sides.
Pak choi: Season your pak choi and sear, cut side down, in a pan preheated on medium heat, ~3-4min. Place a weight or something heavy on the pak choi to get a better crust. Flip the pak choi over, add a splash of water and place a lid on your pan. Let the pak choi steam for ~3min. I like adding a splash of soy sauce and sesame oil at the end and tossing the pak choi.
I found the instructions to be confusing and some steps were missing.