Cut off the stem end and remove skin from onion. Cut in half through the root end; place halves, cut sides down, on cutting board. Working one half at a time, make three to four horizontal cuts parallel to the cutting board, starting at the stem end and stopping each time before cutting through the root. Continue by making equally spaced vertical cuts perpendicular to the root, again, not cutting through the root. Turn the onion 90 degrees and finish by making cuts perpendicular to the last set of cuts, resulting in perfectly chopped onions.