In a 13x9-inch baking dish, combine buttermilk and hot sauce. Add chicken to dish, making sure meat is submerged. Cover with plastic wrap and refrigerate at least 4 hours.
In a large cast-iron skillet, pour oil to a depth of 1 inch. Heat over medium-high heat until a deep-fry thermometer registers 350°.
In a separate 13x9-inch dish, stir together flour and Creole seasoning. Working in batches, remove chicken from buttermilk mixture. Dredge chicken in flour, turning to coat. Fry chicken until browned on each side and a meat thermometer inserted in thickest portion registers 160°. Let drain on paper towels.
To assemble sandwiches, spread 1 teaspoon mustard on bottom half of each bun. Top with a fried chicken cutlet, Mardi Slaw, and the top half of bun.