Trim chicken thighs of any excess fat or cartilage. Combine buttermilk with half the Spicy Mango Hot Sauce and cover chicken thighs in a glass bowl or baking dish. Refrigerate and leave to marinate at least 4 hours, or overnight if possible.
Remove chicken from refrigerator and turn fryer to 350 degrees. If frying on the stovetop, warm several inches of oil in a tall cast iron pot on medium heat making sure to leave plenty of room in the pot for oil expansion and chicken.
Combine flour, cornstarch, Cajun Street blend and salt in a medium bowl.
Remove the chicken thighs from the buttermilk and Hot Sauce mixture allowing excess to drip back into the bowl. Transfer thighs to bowl of seasoned flour making sure to coat the outside well. Remove from flour letting excess to fall back into bowl.
Return to buttermilk one more time, coating the entire outside again. Remove from liquid and place in seasoned flour bowl once again. Coat the thighs well, pressing flour into the chicken to ensure it adheres.
If frying on the stovetop, check oil temperature by dipping a small portion of one chicken thigh into the oil. It should not be smoking but it should begin to sizzle on contact. Carefully place the chicken into the oil and allow to fry for about 6 - 10 minutes, or until chicken is cooked through and crispy. Remove from oil and place on a rack or paper towels to drain any excess grease.
While the chicken fries, warm a large skillet or griddle. Melt the butter and toast each bun until golden brown.
To assemble the sandwiches start with aioli on the bottom bun, follow with a piece of fried chicken, top with hot sauce and pickled onions, then finish with the top bun. Enjoy!