The diner-counter dream: buttermilk-brined thighs in a craggy, double-dredged crust, fried shatter-crisp and stacked with pickles and spicy mayo on a toasted bun.
Whisk the buttermilk, hot sauce, salt, and pepper, then submerge the thighs and brine at least 1 hour, or overnight in the fridge. The acid tenderizes and seasons all the way through.
Stir the dredge ingredients together, then drizzle in the 2 tbsp buttermilk and rake it with your fingers so little clumps form. Those clumps fry into the craggy crunch.
Lift each thigh from the brine, letting the excess drip off, and press it firmly into the flour, coating every fold. For extra armor, dip it back in the brine and dredge a second time.
Heat 1.5 inches of oil in a heavy pot to 350F. Hold the oil at 340 to 350F; too cool and the crust turns greasy, too hot and it browns before the thigh cooks through. Fry two pieces at a time, 5 to 6 minutes, turning once, until deep golden and the center hits 165F. Drain on a rack, not paper, so the bottom stays crisp.
Stir the mayo with the hot sauce. Spread it on both toasted bun halves, then stack lettuce, pickles, and a piece of fried chicken. Press the top on and eat it while it's loud and crisp.