Prepare the Brine: Combine 1 cup buttermilk and 2 teaspoons salt in a container. Add chicken and ensure it's fully submerged. Marinate for at least a few hours, ideally 6, in the fridge.
Make the Slaw: Mix shredded cabbage and carrots. Combine equal parts mayonnaise, sour cream, and red wine vinegar for the dressing. Season with black pepper.
Prepare the Dredge: Mix 1.5 cups flour, 2 tablespoons cornstarch, 2 teaspoons baking powder, 2 tablespoons garlic powder, and chipotle powder or cayenne to taste.
Dredge the Chicken: Let excess buttermilk drip off the chicken, then coat in the flour mixture. Ensure it's fully covered.
Fry the Chicken: Heat oil to 350°F and fry chicken until it reaches an internal temperature of 165°F, or at least 155°F for a minute.
Assemble the Sandwich: Place spicy mayo on both sides of the bun, add a layer of pickles, the fried chicken, top with coleslaw, and cover with the top bun.