Marinate Chicken: Whisk together buttermilk, hot sauce, and salt until salt dissolves. Place chicken pieces in a bag and pour marinade over. Remove air, seal, and marinate for 1-2 hours.
Prepare Breading: Strain chicken from marinade and let drip. Mix flour, Cajun seasoning, and cayenne pepper to create a spice blend. Coat chicken evenly with the flour mixture. Let coated chicken sit for at least 1 hour until coating becomes tacky.
Make Buttermilk Biscuits: Keep butter cold by freezing and grating it. Sift flour, sugar, baking powder, baking soda, and sea salt into a bowl. Add buttermilk and grated cold butter. Mix lightly until dough just comes together. Fold dough on itself a few times gently. Pat dough to about 1 inch thickness. Cut biscuits using a cutter or glass, ensuring biscuits touch each other on the baking tray. Chill biscuits in fridge for 20 minutes.
Prepare Honey Butter: Whisk softened unsalted butter until smooth. Add honey and salt, whisk until combined.
Bake Biscuits: Preheat oven to 425°F (220°C). Bake biscuits for 8 minutes. Remove, brush with honey butter and sprinkle coarse sea salt. Return to oven for 4 more minutes until golden.
Fry Chicken: Heat oil to 350°F (175°C). Fry chicken starting with the largest pieces first (breast), then thighs, and finally smaller drumsticks to maintain oil temperature between 300-325°F (150-160°C). Fry for about 10 minutes or until internal temperature reaches 168°F (75°C). Adjust heat as needed.
Finish and Serve: Dust fried chicken lightly with extra Cajun seasoning. Brush hot biscuits with honey butter. Let chicken rest for at least 8 minutes before serving. Serve chicken with biscuits and honey butter.