Trim the papery skin and the stem end from the onion. Removing the skin first will keep harmful bacteria from the outside of the onion from being transferred into the onion when it is cut in half.

Stand the onion on the stable cut end. Cut through the root end in the center of the onion.

This will create two equal halves held together by the stem.

Lay one half flat on the cutting board. Place your hand on top of the half. Make several equal-spaced, horizontal cuts. Do not cut all the way through. Rather, leave the stem end in tact so that it will hold the layers together.

Turn the onion toward you. Make several equal-spaced vertical cuts once again leaving the stem end in tact.

Starting at the cut end, make equal-spaced cuts parallel to the cut end. This will release the diced onion in square pieces.