In a small bowl combine ketchup, brown sugar, mirin, Worcestershire sauce, ginger, and finely minced garlic. Stir to combine. It is best if you let this rest at least 30 minutes before serving.
Katsu Chicken Preparation
Place halved chicken breast between some plastic wrap and gently pound out the chicken. You want it to be about ¼ inch thick.
Salt the chicken liberally, cover, and place in the refrigerator for about 1 hour. This will help the chicken break down and become super juicy. You could omit this step, but the chicken will come out better if you let the chicken 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.
Coat the chicken as follows:Place in the flour then shake off any excess.Dip into the egg wash, coat well, then shake off any excess.Dredge in Panko breadcrumbs. Place the coated chicken on a wire rack.
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 chicken. Turn the oven on, and preheat to 200 degrees.
Add the chicken 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 chicken and flipping it over until it is golden brown on both sides.
Remove the chicken and place on a clean wire rack. Place into the preheated oven to finish cooking. Depending on the thickness of your chicken, the chicken may need another 7 or 8 minutes of cooking. Chicken should be 165 degrees before consuming.
When the chicken is fully cooked, cut into thin strips that you can pick up with chopsticks. Serve with rice, tonkatsu sauce, or your favorite brown sauce.