To cook the chicken, Prepare your breading station. In a shallow dish, combine the buttermilk with salt, pepper, and cayenne powder. In a separate shallow dish, combine the flour with cornstarch, garlic powder, paprika, salt and pepper.
For extra flaky chicken sandwich, add a tablespoon or so of the buttermilk mixture to the flour mixture, and mix with your hands to create little clumps.
Dredge the chicken in the buttermilk mixture, followed by the flour mixture. Press the chicken into the flour mixture to make sure it sticks to the chicken.
Lightly shake off any excess flour, and place on a plate but do not pile the chicken.
Heat vegetable (or canola) oil to 350°F/180°C in a skillet or a deep fryer. And fry for 3-4 minutes per side, the chicken is ready when the internal temperature reaches 165°F/74°C.
To make the spicy mayo, whisk the ingredients in a small bowl, and set aside.
To toast the brioche buns, melt 1 tablespoon butter to a skillet on medium high heat, and place one bun cut in half cut-side down. Toast until they’re golden brown but not burnt. Repeat with the second bun.
To assemble the chicken sandwich, spread 1 tablespoon of spicy mayo on each half bun, then on the bottom bun layer dill pickle slices over the sauce, place the chicken on top of the pickles, and cover with the top half bun.