In a bowl, whisk the buttermilk with a pinch of salt and pepper. Submerge the chicken pieces and let them soak for at least 30 minutes, or up to 4 hours in the fridge to tenderize.
In a large resealable bag or bowl, combine flour, cornstarch, paprika, garlic powder, onion powder, salt, and pepper. Mix well to create a seasoned dredge.
Heat oil in a deep, heavy pot or dutch oven to 350°F (175°C). You’ll want enough oil for the chicken to float without touching the bottom.
Remove each piece from the buttermilk, letting excess drip off, then dredge thoroughly in the seasoned flour–cornstarch mixture. Shake off any excess.
Fry the chicken in batches, turning once, until deeply golden and the internal temperature reaches 165°F (74°C), about 6–8 minutes per piece depending on thickness. Transfer to a rack or paper towels to drain.
While the chicken rests briefly, prepare the Nashville hot glaze. In a small saucepan, melt 2 tablespoons of butter with 1/4 cup hot sauce (you can use a cayenne-forward hot sauce or a blend). Stir until combined and glossy.
Brush or spoon a generous amount of hot glaze over the fried chicken. If you like it extra spicy, add a touch more hot sauce or a pinch of cayenne to kick it up.
Assemble the sandwiches: spread a thin layer of mayonnaise on the toasted brioche buns, add the glazed chicken, and top with pickles and any slaw you enjoy. Cap with the other half of the bun.