Toast the bread (only until you get a light golden brown color just like on the photo).
Butter each slice of bread.
Spread some Dijon mustard on one slice of each sandwich, according to taste. Place half of the thinly shredded cabbage on the Dijon mustard side and drizzle 2 tsp of Tonkatsu Sauce over the cabbage.
Place the tonkatsu slice on top of the cabbage.
Evenly distribute the remaining cabbage on top of the meat and drizzle another 2 tsp Tonkatsu sauce on it.
Place the other slice of bread on top of your Tonkatsu, butter side down. To make the sandwich flat, put something heavy on it.