Place the beaten egg, flour, and panko in separate bowls. The bowls should be large enough to be able to coat the pork in later on.
Lightly score (shallow cross-hatched cuts) the pork fat on each piece of pork.
Heat up the oil in a frying pan (about 170 degrees Celcius).
Lay four pieces of the pork onto a flat surface (plate, cutting board, etc).
Fold a piece of sliced cheese in half and then place it onto the pork. Repeat for the remaining three pieces of pork.
For toddlers: Fold one perilla leaf in half and place it on top of the cheese on each piece of pork. Then place another piece of pork on top, sandwiching everything inside. (Toddlers will have only two layers of pork, one on the top and one on the bottom.)
For adults: Layer another piece of pork on top of the cheese on each piece of pork. Then fold one perilla leaf in half and add it to each piece of pork. Place the remaining pieces of pork on top of each of the four pieces of pork. (Adults will have three layers of pork — top, middle, bottom.)
Coat the four pieces with flour, then dip it into the beaten eggs and lastly the panko. Make sure to press the panko into the pork so it sticks.
Check if the oil in the pan is hot. One way to do this is to drop a very small amount of panko into the pan. If it sizzles, it's ready. Carefully place the pork cutlets into the oil. (We cook two pork cutlets at a time but of course, this depends on the size of your pan.)
Fry the pork cutlets until the crust is golden. Flip and fry until the other side is golden as well. (about one to two minutes on each side.)
Take the cutlets out of the pan and lay them onto a wire rack or paper towel to absorb the excess oil.
Top with tonkatsu sauce if desired and serve with salad, rice, and miso soup.