a day or 2 in advance...
Stir 3 tablespoons of buttermilk into a pint of milk. (use a pint canning jar). Cover the jar and place it in a warm spot overnight. Check around, you can probably find a warm spot somewhere. Needs to be 80-90 degrees. You can always fill up a 2 liter pop bottle with hot tap water and put it and the jar in an ice chest. You can store the resulting yogurt/buttermilk in the fridge for about 3 weeks. Use most of it for the marinade but reserve about 3 tablespoons and refill the jar. You can also refill the jar with cream instead of milk which makes wonderful sour cream/creme fraiche.
Also, the morning before you fry the chicken make hamburger buns.
2 large skinless chicken breasts - Slice each breast into 3 pieces so they are somewhat thin, about 3 inches by 4 inches. Marinate the 6 chicken pieces for 3-4 hours. After marinating, remove the chicken pieces and whisk an egg into the leftover marinade.
Using 2 forks dip the chicken pieces back into the leftover marinade and into the breading. Now dip again and bread a second time. Let chicken pieces sit for 15 minutes for the breading to hydrate.
Heat an inch of oil to ~350 in a large cast iron pan. Fry 3 pieces at a time about 3 minutes per side. Drain on wire rack. Serve on hamburger buns with pickle slices and mayonnaise.
This is not exactly Chef John's recipe. Sometimes you have to correct him!