To make authentic Japanese curry, be sure to source the ingredients listed before using substitutes. However, if you can’t check everything off your list, some alternatives still taste good. If you can’t find instant dashi, which is a powdered flake that can be boiled in water to easily create a dashi base, choose homemade dashi, fish dashi, or chicken dashi.
Curry roux, the main ingredient in curry udon, is difficult to substitute. The closest thing to this would be a bouillon cube, but even that doesn’t look like it. Instead, the easiest way is to make the roux yourself from scratch. This is achieved by cooking flour, butter, spices and curry powder together until golden brown. The challenge, of course, is finding a Japanese curry powder that tastes similar. You may want to make your own blend of cardamom, cinnamon, cumin, turmeric, and other spices.
The last essential ingredient for curry udon is, you guessed it, udon noodles. If you can’t find vacuum-sealed frozen or refrigerated udon noodles, the next best option is to look for shelf-stable or dried udon noodles. Dry udon noodles take a little longer to boil and have a texture a bit similar to linguine, but with udon’s characteristic spongy feel. If you can’t find udon, you can substitute ramen, spaghetti, or linguine.