Mix buttermilk, hot sauce, 1 teaspoon kosher salt, and black pepper in a large bowl. Add the chicken, cover, and refrigerate for at least 4 hours or preferably overnight.

Whisk flour, cornstarch, paprika, garlic powder, onion powder, cayenne, baking powder, and the remaining 1 teaspoon salt in a wide bowl.

Remove chicken from the buttermilk, let excess drip away, and dredge thoroughly in the flour mixture. Press the coating onto each piece, then dip briefly back into the buttermilk and flour again for a thicker crust if desired.

Heat 2 quarts of oil in a heavy Dutch oven or deep skillet to 350°F. Fry in batches while keeping the oil between 325°F and 350°F, cooking breasts about 12–15 minutes and thighs, drumsticks, or wings about 10–14 minutes.

Transfer fried chicken to a wire rack over a baking sheet and cool completely for 20–30 minutes. Freeze the pieces uncovered in a single layer for 1–2 hours, wrap each piece tightly, and store in a freezer bag or airtight container.

Reheat frozen chicken uncovered on a wire rack at 400°F for about 20–25 minutes, turning once if needed, or air-fry at 375°F for approximately 10–15 minutes. Confirm that the thickest part reaches 165°F before serving.