It is practically impossible to learn how to cook without knowing how to dice an onion. They’re an essential allium; the base upon which millions of recipes have been built. Add some carrots and celery to your diced onions, and you’ve got a French mire poix; add garlic and tomato instead, and that’s a Spanish sofrito. It’s an integral element in cuisines from West Africa to Southeast Asia, from the Indian Subcontinent to North and South America. In fact, you could make a good argument that the onion is the world’s most beloved vegetable. You may not always be able to taste onions in any given recipe, but you will most always notice when they’re missing.
As you may already know, dicing onions can make your eyes water up something awful; this is because cutting breaks open onions’ cell walls, releasing amino acids and enzymes that, when mixed, turn into a chemical vapor that burns your eyes and forces them to well up with tears. While there’s no shortage of “miraculous” hacks around this annoying problem — like sticking your tongue out while cutting onions, or wearing a motorcycle helmet — the best way to avoid keep your eyes dry is by using a super-sharp knife, which will keep the number of shattered cell walls to a minimum.
Along with your sturdy, well-sharpened knife, you will also need a proper cutting board that doesn’t wobble. Slide a wet paper towel underneath your cutting board to keep it from sliding all over the countertop.
Here's everything you need to know to easily dice an onion.
How to Dice an Onion in 4 Simple Steps
- Holding it at the root end, slice off the top of the onion and toss it in the compost pile. Next, set the onion cut-side down, with the root sticking up, and slice the onion in half in one clean cut. Peel the papery skin off each half, as well as any layers that feel tough, dried-out, or rubbery.
- Put the onion halves cut-side down with the root end pointing away from you. Use your knuckles to firmly hold each half down as you make a few cuts with your knife parallel to the board, stopping before you cut all the way through the root. For a large dice, make these cuts about ¾-inch wide; for medium dice, ½-inch; small dice, ¼-inch.
- Next, make several vertical cuts through the onion, spacing as written above, and, again not cutting through the root.
- Finally, rotate the onion halves and slice the onion to the correct thickness; as you cut, perfectly diced pieces will fall away from the knife.