Step 1

Preheat oven to 175°F. Arrange chicken in a single layer on a large cutting board and cover with plastic wrap. Gently pound with the flat side of a meat mallet or the bottom of a heavy skillet to an even 1/4-inch thickness. Season chicken on both sides with salt and pepper.

Step 2

Place flour in a pie dish or a wide, shallow bowl; season with salt and pepper. Whisk egg in another dish until thoroughly combined (no clear streaks remaining). In a third dish, combine panko with sesame seeds and dill; season. Working one at a time, dredge chicken pieces in flour, turning to evenly coat and shaking off any excess. Dip in egg, turning to evenly coat and allowing any excess to drip back into dish. Dredge in panko mixture, turning and pressing with your hands as necessary to fully coat. Transfer to a rimmed baking sheet lined with a wire rack and let stand 10 minutes.

Step 3

Heat 1/4-inch oil in a large, heavy skillet (preferably cast iron) over medium-high. When it shimmers, carefully add 1 or 2 cutlets in a single layer (do not crowd pan). Cook, flipping once, until chicken is just cooked through and panko turns crisp and golden brown, 4 to 6 minutes total (if panko begins to darken too quickly, reduce heat slightly). Transfer to a wire rack set inside a rimmed baking sheet and keep warm in preheated oven while frying remaining pieces. Serve, with relish and mustard alongside.