This is real homemade tonkatsu sauce from scratch! It takes some effort, but the result is so worth it! The strained bits can be added to curry or hamburger steaks as a hidden flavor.
When I used to live overseas, I was unhappy with the sauces available at the supermarket, so I recalled how to make the sauce from scratch and recreated the recipe from memory!
Simmer over low heat, making sure not to let it burn. I've flavored it so that it's close to a sweet demi-glace. I think the flavoring depends on ones individual taste.
Enjoy Japanese food around the world.