If necessary, butterfly or gently pound the chicken breasts so the thickest sections are relatively even.
In a large bowl, whisk together the buttermilk, egg, and 1 tablespoon all-purpose chicken seasoning.
Add the chicken and turn until thoroughly coated.
In a shallow dish, combine the flour, cornstarch, baking powder, salt, and remaining tablespoon of chicken seasoning.
Lift one piece of chicken from the wet mixture and let the heavy excess drip away.
Place the chicken into the dry mixture and coat thoroughly, pressing the breading firmly onto both sides.
Repeat with the remaining chicken.
Heat the peanut oil in a deep skillet to approximately 350°F (175°C).
Carefully fry the chicken in batches, turning as needed, until the coating is deeply golden and crispy.
Check that the thickest part of each piece reaches 165°F (74°C).
Transfer the chicken to a wire rack and let the excess oil drain.
Combine the shredded cabbage and carrots in a bowl.
Stir together the mayonnaise, white vinegar, sugar, and salt.
Add the dressing to the vegetables and toss until lightly coated.
Lightly toast the brioche buns if desired.
Spread honey dijonnaise over the bottom buns.
Add the crispy chicken and Swiss cheese.
Top with tangy slaw, pickles, and optional jalapeños or bacon.
Drizzle with more honey dijonnaise, add the top bun, and serve immediately.
