Soak. Add 1 teaspoon of salt to the buttermilk in a large bowl and mix well. Then, submerge the chicken thighs in the buttermilk mixture. After that, cover the bowl and refrigerate for at least 6 to 12 hours.
Bread. In a large zipper bag or a big paper bag, mix the flour, 2 teaspoons salt, pepper, garlic powder, and cayenne pepper. Then, take the chicken thighs out of the buttermilk, shaking off any extra liquid. Next, put the thighs into the bag with the seasoned flour mixture. Close the bag and shake it until the chicken is coated well. Put the coated chicken on a plate or tray and refrigerate for 1-2 hours to help the breading stick better.
Fry. Preheat your deep fryer to 340°F (or use a heavy-duty Dutch oven filled with three inches of oil and a candy thermometer to monitor the temperature). Carefully place the chicken thighs into the hot oil. Then, cover and fry the chicken for 12-15 minutes on each side until the coating is golden brown and the inside reaches at least 165°F.
Hold or serve. Place a cooling rack on top of a baking sheet lined with paper towels. Then, transfer the fried chicken to the rack to let any extra oil drip off. You can serve the chicken right away or keep it warm in an oven set at 200°F until you're ready to serve.