Step 1

Whisk 1 Tbsp. salt, 2 tsp. black pepper, paprika, cayenne, garlic powder, and onion powder in a small bowl. Season chicken with spices. Place chicken in a medium bowl, cover, and chill overnight.

Step 2

Let chicken stand covered at room temperature for 1 hour. Whisk buttermilk, egg, and 1/2 cup water in a medium bowl. Whisk flour, cornstarch, remaining 1 Tbsp. salt, and remaining 1 Tbsp. pepper in a 9x13x2" baking dish.

Step 3

Pour oil into a 10"–12" cast-iron skillet or other heavy straight-sided skillet (not nonstick) to a depth of 3/4". Prop deep-fry thermometer in oil so bulb is submerged. Heat over medium-high heat until thermometer registers 350°. Meanwhile, set a wire rack inside a large rimmed baking sheet.

Step 4

Working with 1 piece at a time (use 1 hand for wet ingredients and the other for dry ingredients), dip chicken in buttermilk mixture, allowing excess to drip back into bowl. Dredge in flour mixture; tap against bowl to shake off excess. Place 5 pieces of chicken in skillet. Fry chicken, turning with tongs every 1–2 minutes and adjusting heat to maintain a steady temperature of 300°–325°, until skin is deep golden brown and an instant-read thermometer inserted into thickest part of chicken registers 165°, about 10 minutes for wings and 12 minutes for thighs, legs, and breasts.

Step 5

Using tongs, remove chicken from skillet, allowing excess oil to drip back into skillet; transfer chicken to prepared rack.

Step 6

Repeat with remaining chicken pieces; let cool for at least 10 minutes before serving.