So, it always has to have apples in it? This blogger says it can have anything you want in it and gives some examples.
sudachirecipes.com/japanese-curry-roux-cubes/
Japanese Curry Using Roux Cubes (including lots of secret tips) - Sudachi Recipes
Make the ultimate Japanese curry rice at home using roux cubes with my step by step guide, secret ingredients and favourite toppings!
