Step 1

Stir together 4 cups water, 1/4 cup salt, peppercorns, and bay leaf in a medium saucepan; bring to a boil over medium-high. Meanwhile, place ice cubes in a large heatproof container. Once water-spice mixture comes to a boil, remove from heat, and carefully pour over ice. (This allows the brine to cool quickly and become ready to use.) Lay chicken breasts flat on a cutting board, and pat dry with paper towels. Working with 1 chicken breast at a time, place your non-dominant hand flat over top of chicken breast, and apply a good amount of pressure so the breast stays in place. Using a sharp knife, cut breast in half horizontally, stopping just as you get to the opposite side. (Do not cut all the way through.) Open chicken breast like a book. (Both sides should be of equal thickness to ensure even cooking.) Repeat butterflying process with remaining breast. Transfer butterflied chicken breasts to container with cooled water-spice mixture; cover and refrigerate 3 hours.

Step 2

Remove chicken breasts from brine, and transfer to a medium bowl; discard brine. Pour buttermilk over chicken breasts to cover. If needed, place a small plate on top of chicken breasts to keep them submerged. Cover with plastic wrap, and refrigerate 2 hours.

Step 3

Whisk together flour, onion powder, and 2 teaspoons salt in a large, shallow bowl. Remove chicken breasts from buttermilk, letting excess drip back into bowl. Dredge chicken breasts in flour mixture, shaking off excess; transfer to a wire rack set inside a baking sheet. Reserve flour mixture in bowl. Cover chicken on baking sheet and flour mixture in bowl; transfer to refrigerator, and chill at least 1 hour or up to 12 hours.

Step 4

Remove chicken and flour mixture from refrigerator. Dredge chicken 1 more time in reserved flour mixture, shaking off excess. (Chicken will be slightly moist; the second dredge is for soaking up the remaining buttermilk goodness.)

Step 5

Pour oil into a 12-inch cast-iron skillet to a depth of 1 inch, and heat over medium to 325°F, adjusting heat as needed to maintain oil temperature. Carefully add 1 chicken breast to hot oil, and cook until bottom side is golden brown and crispy, 3 to 5 minutes. Carefully flip chicken, and continue frying until both sides are golden brown and crispy and a thermometer inserted in thickest portion of chicken registers 165°F, 3 to 5 minutes. Transfer fried chicken to a plate lined with paper towels, and sprinkle with 1/4 teaspoon salt. Repeat frying process with remaining chicken breast and remaining 1/4 teaspoon salt. Serve immediately.