Prepare the marinade by whisking together the hot sauce, buttermilk and ground mustard in a medium-sized bowl. Set the marinade aside.
Place the chicken thighs or breasts in a casserole dish, and pour the buttermilk mixture over them. Let the chicken marinate in the refrigerator for 1-4 hours, or overnight.
Prepare the buttermilk-ranch sauce by whisking together all of the sauce's wet ingredients with the dry seasonings. Stir in the fresh chives and dill. Set aside, or chill in the refrigerator.
Prepare the seasoned coating by whisking together the flour, cornstarch and dry seasonings in a large bowl.
Pre-heat the oil to 350°F in a deep-sided dutch oven or large cast iron skillet.
Remove the chicken from marinade, shake off any excess marinade and set the chicken aside. Add 1 egg to the bowl of leftover marinade and whisk until the egg is fully disbursed.
Dredge each chicken breast/thigh in the seasoned flour, dip once more in the marinade and let the excess marinade drip off, then dredge in flour again.
Drop each breast/thigh in the hot oil and fry for 15-18 minutes. You can fry all 4 pieces of chicken in the same batch. Use a digital meat thermometer to measure the internal temperature of the chicken. The temperature needs to register at 170°F for thighs and 165°F for breasts.
Assemble the sandwiches in this order: Bottom bun, a thin layer of ranch, a few pickle chips, crispy chicken, another spoonful of ranch, shredded iceberg, a few more pickle chips, top bun.