How to Make It
In a bowl, combine the salt, pimentón, garlic and pepper. Add the chicken and rub all over with the spices. Add the buttermilk and turn to coat. Cover with plastic wrap and refrigerate overnight.
In a small skillet, toast the coriander, cumin, caraway, oregano, peppercorns and red pepper over low heat, stirring, until very fragrant, 3 minutes. Transfer to a spice grinder, let cool slightly, then finely grind. Transfer to a bowl and whisk in the pimentón, garlic, salt and all-purpose flour. Transfer half of the flour mixture to another bowl and whisk in the rice flour and cornstarch.
Drain the chicken, reserving the buttermilk. Coat the chicken in the seasoned all-purpose flour, shaking off any excess. Set on a rack and refrigerate for 1 hour. Let stand at room temperature for 15 minutes.
In a large enameled cast-iron casserole, heat 3 inches of oil to 325°. Dip the chicken in the reserved buttermilk, then dredge in the rice flour mixture. Fry in 2 batches, turning, until the dark meat registers 155° on an instant-read thermometer and the breast meat registers 150°, about 15 minutes for the dark meat and 20 minutes for the breast. Transfer to a rack and let cool, then refrigerate until cold.