Combine all ingredients for buttermilk. Whisk well to combine. Marinade the chicken in buttermilk mix for at least an hour.
Whisk together ingredients for flour. Take chicken out of buttermilk and drench in seasoned flour. Place on baking sheet or plate and leave out for at least 15 minutes. Fry chicken at 360F for 15 minutes or until cooked all the way through.
For the Gochujang Mustard Miso: Combine miso paste, garlic, brown sugar, and 1/4 cup water in small saucepan. Bring to a simmer over medium heat. Cook 1 minute, or until miso dissolves and begins to bloom. Remove from heat; stir in oil and vinegar. The fold in mustard and gochujang paste.
Serve freshly fried chicken with gochujang mustard miso and bibb lettuce cups.