With a sharp chef's knife, remove the stem and blossom ends of the onion.
Stand the onion on one of the cut ends and slice it in half vertically. Remove the skin.
Place cut side down, with the trimmed ends parallel to your shoulders + perpendicular to the edge of the counter. Draw the blade through the onion 3-4 times. Leave the starting edge intact.
Rotate the onion 90 degrees, and draw the knife through it following the contour of the onion, slicing the onion into a small dice.
When you come to the intact edge, tip the onion over and dice it with two or three slices.
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