Slice each chicken breast lengthwise (parallel to your work surface) into two pieces. Season both sides with salt and pepper.
2 boneless, skinless chicken breasts, ½ teaspoon kosher salt, ¼ teaspoon ground black pepper
Create a breading station. Add the flour, eggs, and Panko each to separate shallow bowls.
½ cup all-purpose flour, 2 large eggs, 1½ cups Panko breadcrumbs
Dredge the chicken in the flour, shaking off excess; then the eggs, letting any excess drip off; and finally, the Panko.
Fill a large cast iron skillet with ¼-inch oil. Heat over medium until it reaches 350°F.
1 cup vegetable oil
Place the chicken, 2 pieces at a time, into the oil, cooking on both sides until golden and 165°F internally, about 2 minutes per side. Transfer to the prepared plate and repeat with remaining chicken breasts.
Serve hot with tonkatsu sauce.
Tip: If the Panko breadcrumbs aren't sticking well to the chicken, gently press them onto the surface of the chicken to help them adhere. Adding a teaspoon of oil to the egg can also help the breadcrumbs to stick better.
Storage: Store chicken katsu in an airtight container in the refrigerator for up to 3 days or in the freezer for up to 3 months. Store leftover tonkatsu sauce in an airtight container in the refrigerator for up to 1 month.