Let’s be brutally honest here: there is no “one Japanese curry recipe.” There’s historical recipes. There’s common recipes. There’s also the fact that everyone who is a fancier, every restaurant, every region of Japan, has their own recipe or recipes. Curry is a phenomena there, one comprable to mania for chili or barbecue in America.
The very basic japanese curry is a fat or oil, flour, and curry powder mixed into a roux, at times with some other things. Then broth is added (often from vegetables and meat being prepared at the same time). The roux is mixed into the broth, and oftentimes returned to the pot the other ingredients are in so it cooks together.
Now as my goal is to make a curry sauce that can be made and used any time (without preparing other ingredients), and make it low-fat/low sodium, my quest was a bit different. With some digging and comparing, I was able to make a “composite” basic Japanese curry recipe below.