Variations on this tangy-sweet, fruity-savoury, Worcestershire-like brown sauce – an essential flavour in dishes like okonomiyaki, takoyaki, tonkatsu and yakisoba – are incredibly common in casual modern Japanese cooking. I was running a cooking class a while ago in which I taught the students how to make this, and one of them said, upon tasting it, ‘Oh! You taught us how to make brown sauce.’ And so I did – tonkatsu sauce’s flavour is remarkably British, sitting somewhere on the flavour spectrum between HP and Branston Pickle, but it has a few Japanese flourishes to enhance umami and sweetness. It also has a delightful affinity with mayonnaise.
By the way, there’s no need to get too nerdy about this, but generally speaking this sauce should be made a little sweeter for okonomiyaki (more sugar), more acidic for tonkatsu (more vinegar/Worcestershire sauce), and thinner and more savoury for yakisoba (more soy sauce/ Worcestershire sauce).
Not difficult