Combine the thighs, buttermilk and 1 teaspoon salt and refrigerate for 2 to 8 hours.
Whisk the rice flour, all-purpose flour, paprika, thyme, garlic powder, cayenne, white pepper and remaining salt in a shallow pan.
Shake excess buttermilk from each thigh, press it into the flour mixture and rest the coated chicken for 10 minutes.
Heat 1 1/2 inches peanut oil in a heavy pot to 340°F.
Fry the thighs in two batches for 5 to 7 minutes per side, holding the oil between 330°F and 345°F.
Remove the chicken when the coating is copper brown and the center reaches 165°F, then drain on a wire rack.
Rest for 6 minutes before serving so the thin crust finishes crisping.