In a large bowl, stir together 10 cups water and 2 Tbsp salt. Add the chicken covering all pieces with brine solution. Cover and refrigerate overnight.
In another bowl, whisk together kefir, 1 Tbsp salt, mustard, paprika, ½ cayenne pepper (if using) and ½ tsp black pepper.
Transfer chicken from the salt brine to the marinade. Cover and refrigerate for at least 4 hours and up to overnight.
Remove the chicken from refrigerator an hour before frying - let stand at room temperature.
Mix together flour, cornmeal, 1 tsp black pepper and ½ tsp cayenne pepper (if using).
Whether using a deep fryer or oil in heavy pot (filled halfway with oil), heat oil to 350F.
Remove chicken from the marinade a few pieces at a time - do not shake off excess - dredge in flour mixture.
Fry chicken in batches until golden brown and thermometer inserted in the thickest part reads 160F. It takes about 10 minutes depending upon the size of pieces.
Transfer to wire rack.
Serve and enjoy!
Be sure to allow the oil to reheat between batches.
Do not stack chicken on paper towel - this causes the crust to become soggy.
The brining of the chicken is an important step to seal in the moisture so, don't skip it! It sounds really fancy but it is simply soaking the chicken in a salt bath.
With the chicken, it actually soaks in some of the salt so, no salt is necessary in the flour used to dredge it before frying. It does take planning ahead to brine it, but trust me, the results are worth it.