Place the 4 small skinless, boneless chicken breasts on a cutting board and pound each to an even 1/2-inch thickness.

Season both sides of each breast with the 1/2 teaspoon salt and 1/4 teaspoon pepper, then drizzle the 2 tablespoons soy sauce over the breasts.

Set up three shallow bowls: add the 2 tablespoons all-purpose flour to the first bowl, the whisked 1 large egg to the second bowl, and the 1 cup panko breadcrumbs to the third bowl.

Working with one piece at a time, dredge a chicken breast in the flour, shake off any excess, dip it in the whisked egg, then press it into the panko so it is evenly coated. Repeat with the remaining breasts.

Pour 1/2 cup oil into a non-stick skillet and heat over medium-high heat until the oil reaches 350°F (or is shimmering and hot).

Carefully add the breaded chicken breasts to the hot oil without crowding the pan. Fry for 4–5 minutes total, flipping once about halfway through (about 2–2.5 minutes per side), until the crust is golden brown and the internal temperature reaches 165°F.

Transfer the cooked chicken katsu to paper towels to drain excess oil. Let rest briefly, then slice and serve with the 1/2 cup katsu sauce.