Marinate your chicken in milk marinade for 8-12 hours in the fridge.
Place flour, beaten egg, and panko crumbs into separate shallow dishes. Coat chicken breasts / tenderloins in flour, shaking off any excess; dip into egg, and then press into panko crumbs until well coated on both sides.
Pack 6-7 pieces of tenderloins as one meal to make taking it out + thawing easier. Place them in a ziplock bag and in the freezer.
Leave them out in room temp for 2 hours to defrost.
Add your oil of choice to a pan over medium low heat and when the oil is heated, add your katsu pieces.
Fry on each side for a total of 5-6 min until golden brown and the chicken is cooked through.