Place the chicken in a shallow dish.
Add 1 cup of the pickle brine and garlic. Cover.
Refrigerate for at least 8 hours and up to 12.
Line a baking sheet with a rack or paper towels.
Combine the flour, cornstarch, baking powder, garlic powder, salt, black pepper, salt, and cayenne pepper in a shallow bowl.
Add the remaining pickle brine to the flour mixture and work it in with your hands.
Remove the chicken from the brine. Working one piece at a time, and coat with the flour, using your hands to firmly press the flour into the chicken.
Return to the brine and coat again, then re-coat with the flour mixture.
Preheat the oil in a dutch oven, wok or other heavy duty pan to 350°F. Add the chicken, working in batches as necessary, and cook, flipping halfway, until golden brown and an instant read thermometer registers 165°F. Transfer to the prepared baking sheet. Rest for 5 to 10 minutes.
Toast the buns if desired. Spread the mayonnaise or burger sauce on the buns and add the chicken. Top with the desired fixings.