So you want to make Yukihira's Tonkatsu with Black Cheese Sauce, eh? Just be aware...it takes a LONG time to make and if anything you can make a nice béchamel (cheese sauce) and add some roasted ...
You can purchase both types at the store, but you don't need to pony up any cash for distilled water when you ca make it at home – especially if one of it uses happens to be DIY homemade ...