Combine the 1 cup buttermilk and 1 tsp hot sauce in a bag or dish, add the chicken breasts, and refrigerate for at least 30 minutes.

Cook the 8 strips thick-cut bacon in a skillet over medium heat for 4 to 5 minutes per side until crisp, then drain on paper towels.

Whisk together the 1/2 cup mayonnaise, 1 tbsp buttermilk, 1 tsp dried dill, 1/2 tsp dried parsley, 1/2 tsp garlic powder, 1/2 tsp onion powder, and 1 tsp lemon juice, then refrigerate.

Mix the 1 cup flour, 1/4 cup cornstarch, 1 tsp garlic powder, 1 tsp onion powder, 1 tsp smoked paprika, 1 tsp salt, and 1/2 tsp black pepper in a shallow dish. Lift each chicken piece from the brine, shake off excess, press into the flour mixture on both sides, and rest on a wire rack for 5 minutes.

Heat vegetable oil in a heavy pot to 350°F (175°C) and fry the chicken in batches of 2 for 6 to 8 minutes total, turning once, until the crust is deep golden brown and the internal temperature reaches 165°F (74°C).

Toast the 4 brioche buns cut-side down in a dry skillet for 1 to 2 minutes, spread ranch sauce on both halves, then layer lettuce, tomato, fried chicken, and 2 strips of bacon on each bun and serve immediately.