For the buttermilk marinade - Place chicken in a large bowl, add in cayenne, paprika, celery, garlic, hot sauce, salt and pepper. Use hands or a wooden spoon to rub the spices into the chicken. Pour in the buttermilk on top of the chicken and gently stir. Make sure the buttermilk completely covers the chicken. Cover the bowl with plastic wrap and refrigerate for at least 4 hours, or even better, overnight.
For the flour coating - In a large bowl, whisk together the flour, paprika, cayenne, garlic, baking powder, salt and pepper. Remove The chicken from the buttermilk marinade, shake off any excess buttermilk from the chicken and place the it on a plate. Leave the buttermilk mixture in its original bowl.
Prepare a large rack with a plate underneath for the chicken. Working one fillet at a time, cover the chicken in the flour mixture and shake off any excess flour. Cover the chicken into the buttermilk mixture and shake off any excess buttermilk. One more time, cover the chicken into the flour mixture, then shake off any excess flour. Place the chicken on the rack and repeat the same steps for all the chicken fillets. Leave the chicken to rest on the rack for 30 minutes at room temperature before frying.
In a wok or saucepan, pour enough oil to deep fry the chicken, place over medium to high heat. Heat the oil to 180°C (356°F) or test the oil by placing a wooden object into the oil (chopstick, skewer or wooden spoon). The oil is ready for frying if it bubbles around the wooden object. Carefully lower two chicken fillets into the oil, use a wire strainer or heatproof spatula to stop the chicken from sinking to the bottom of the pan because it'll burn. Fry the chicken for a few minutes until it's lightly golden and carefully turn it over. Fry each fillet for 8 to 10 minutes, turning the chicken occasionally for even cooking and colour. Place the chicken on a clean rack and quickly place a cheese slice on top so it'll slightly melt. Repeat these steps with the remaining chicken.
In a frying pan, cook the bacon over medium to high heat for 5 minutes or until the fat has rendered.
Toast the insides of the burger buns and butter them. Make the spicy sauce by mixing the hot sauce and mayonnaise together in a bowl. Build the burger starting from the base, add lettuce, chicken fillet with the cheese, 1 1/2 tablespoons of the spicy sauce, bacon and the burger lid.