To me katsu sauce is sort of like ketchup: The homemade version will never beat Heinz. Except, in the case of katsu sauce, the brand is Bull-Dog. The white-capped bottle has been a fixture in my fridge from the time of my very earliest memories, and its flavor is intimately linked to katsu in my mind.

—J. Kenji López-Alt, Serious Eats

If you read today's Quality Linkage column, you now know at least one way to prepare tonkatsu. From there, you might be tempted to go off and make your own sauce to go with it, but as J. Kenji notes (as quoted above), you'd do just as well to buy the pre-made stuff like you would with most condiments.

Tonkatsu sauce can be a bit difficult to find though if you live outside a big city, or if you don't have an Asian supermarket nearby. Make it easy on yourself and just pick up some Bull-Dog sauce. It's sort of like a Japanese version of Worcestershire sauce except it's a bit thicker, richer, and sweeter. This sauce is meant to pair perfectly with tonkatsu but can also be used for other Japanese dishes, such as okonomiyaki and takoyaki.

Now, I know that $8.50 for one 10.1-ounce bottle is on the pricey side, so I recommend picking up a 3-pack for $15.50, which is a much better value (as long as you're sure you'll use it all).