1/4 cup ketchup
1/4 cup apple butter or applesauce
1 tablespoon Worcestershire sauce
1 tablespoon low-sodium soy sauce
1 teaspoon Dijon mustard
1 teaspoon unseasoned rice vinegar
1/4 cup all-purpose flour
2 egg whites, beaten
1 cup panko (Japanese bread crumbs)
Two 8-ounce pork tenderloins, cut into 2-inch pieces and pounded 1/2 inch thick
1/4 cup canola oil
Steamed rice and steamed spinach, for serving
In a saucepan, bring the ketchup, apple butter, Worcestershire, soy, mustard and vinegar to a simmer; transfer to 4 bowls. Cool.
Put the flour, egg whites and panko in 3 separate shallow bowls. Season the pork cutlets with salt, then dredge in the flour, tapping off the excess. Dip the cutlets in the egg white, followed by the panko, pressing the crumbs to help them adhere.
In a large skillet, heat 2 tablespoons of the oil. Add the cutlets and cook over moderate heat until golden brown, about 5 minutes. Brush the remaining 2 tablespoons of oil on the cutlets. Flip and cook until golden and cooked through, about 5 minutes longer. Transfer the tonkatsu to a work surface and cut into strips. Transfer to plates and serve with rice, spinach and the dipping sauce.
MAKE AHEAD The sauce can be refrigerated for up to 1 month.