Make 3-4 tiny slits on the connection tissue between the meat and fat without cutting through the meat.
Pound the meat into thin and an even thickness (about ¼ inch each). Season with salt, and pepper.
Prepare 3 large bowls. Fill the first bowl with flour. Fill the second bowl with beaten egg. Fill the third bowl with panko.
Dredge the meat into the flour, and shake the excess flour.
Dip the meat into the beaten egg, and shake the excess.
Dredge the meat in panko, then covers the meat evenly with panko breadcrumbs by patting it with your hands to make the meat thoroughly covered. Turn it over and repeat. Shake off excess crumbs.
Heat at least 1 ½ inches of oil in a deep, heavy-bottomed pot to 350°F on medium-high heat. Dip a chopstick into the oil. If the oil starts steadily bubbling, then the oil is hot enough for frying.
Working in batches, deep fry the cutlet (one at a time) until golden on the bottom for about 3 minutes. Flip and cook for 2 minutes or until fully cooked. Transfer pork to a paper towel-lined or wire rack to drain.
Tonkatsu Sauce: In a medium bowl, stir in all the Tonkatsu sauce ingredients.