Coat both sides of the fillets with the buttermilk mixture. Let them soak for at least 10 minutes. They can be soaked longer, up to 24 hours, just refrigerate and remove from the refrigerator to the counter for 10 minutes before frying.
Mix the spices into the bread crumbs.
Drain one side of the fillets on paper towels so they aren't quite so wet.
Coat the fillet with the panko and press down, if needed, to make panko adhere to fish.
Add enough oil to get a depth of approximately 1 inch deep, in heavy bottom pan. Bring oil to 350-365°F. Add fillets a few pieces at a time. Don't overcrowd the pan. Fry until golden brown (about 3-5 minutes, depending on thickness) on one side, flip and brown second side.
Drain on wire rack. Serve with sweet potato chips.
Video
Notes
Let filets drain for a few minutes on paper towels before coating with breading.Press the fish into the panko so that the breading adheres to the fish.Place them in the hot oil immediately after breading. Watch the filets carefully, so that they don't over-brown.If you have large filets, they can be finished in the oven at 350°F. Internal temperature should register 145°F