katsu5What is katsu sauce? Katsu (or tonkatsu sauce) is a thick condiment, similar to American BBQ sauce, served with a popular Japanese dish of deep fried pork cutletTuck the chicken katsu in a bun or between two glorious pieces of sandwich bread. Katsu Donburi: Got some leftover chicken katsu? Turn it into katsudon, the rice bowl that makes leftovers even better. How to Store.