Heat a sous vide water bath to 155F degrees.
Season the chicken on both sides with the salt and pepper and place in a sealable bag.
Use a vacuum sealer to vacuum seal the bag, or use a heavy duty ziplock bag along with the water displacement method (see in post instructions above) to remove the air from the bag.
Cook for 90 minutes. (You can leave the chicken in the water bath for up to 3 hours before it will start to become too mushy).
While the chicken cooks, mix together the buttermilk and hot sauce and store in the fridge until ready to use.
Mix the flour, cornstarch, Cajun seasoning and cayenne (if using) in a bowl and set aside
Remove the chicken from the bag and pat dry.
Dip each piece of chicken in the flour mixture and shake off the excess.
Dip in the buttermilk and back in the flour mixture to create a batter.
Heat about 3-4 inches of oil in a Dutch oven to 350F degrees. Gently lower in 2-3 thighs and cook about 3-5 minutes, or until the crust is golden brown.
Remove the chicken and place on a wire rack (with a paper towel underneath) to drain. Sprinkle lightly with flaky sea salt and serve while hot.
Repeat for the second batch.