Picture this: You just moved to a new city, and in an effort to unclutter your life, you brought only the bare essentials to your new apartment. Maybe that includes a kitchen knife. It probably doesn’t include a knife sharpener, though.

But now, through overuse and/or improper care, that one kitchen knife can barely slice through a stick of butter, and you’re too poor frugal to buy something new.

The solution? Some genius realized that the rough porcelain surface of your coffee mug’s bottom is a perfectly suitable knife sharpener. This video shows you how to use it to MacGyver your way to a blade with a like-new edge. That’s assuming, of course, that you have a coffee mug on hand. But of course you do. What could be more essential?