In a small bowl combine ketchup, soy sauce, brown sugar, mirin, Worcestershire sauce, ginger, and finely minced garlic. Stir to combine. It is best if you let the sauce rest at least 30 minutes before serving.
Katsu Pork Preparation
Cut the pork loin into thin slices.
Place each pork loin slice between some plastic wrap and gently pound out the slice. You want it to be about ¼ inch thick.
Sprinkle salt on the pork slices, cover, and place them in the refrigerator for about 1 hour. This will help the pork break down and become super juicy. You could omit this step, but the pork will come out better if you let the pork rest.
Set up a breading station with three bowls.
Place the all-purpose flour into one bowl.
Beat the eggs and 1 1/2 tablespoons of water together very well, and pour into a second bowl.
Place panko breadcrumbs into the third bowl.
Place the pork slices in the flour and coat the entire surface then shake off any excess.
Dip them into the egg wash, coat well, then shake off any excess.
Dredge them in panko breadcrumbs.
Place the coated pork slices on a wire rack.
Preheat the oven to 200 degrees.
Add enough vegetable oil to coat the bottom ½ inch of either an iron skillet or a stainless steel pan and heat to 350 degrees. Your pan should be large enough not to overcrowd the pork.
Add the pork to the pan and cook for 1 to 2 minutes, just until the crust sets. Flip over and cook for another 1 to 2 minutes. Continue cooking the pork and flipping it over until it is golden brown on both sides.
Remove the cooked pork slices from the pan and place them on a clean wire rack, to drain off excess oil.
Then place them into the preheated oven to finish cooking. The pork is still rare at this point, so you should place it into the oven for 8 to 10 minutes so it finishes cooking.
When the pork is fully cooked, cut it into thin strips that you can pick up with chopsticks.
Serve with rice, tonkatsu sauce, or your favorite brown sauce.