While I was writing a recipe for vegetable broth, I realized that it might be helpful to include instructions on cutting an onion. Cutting onions seems to cause a lot of undue strife. It’s not just the tears, it’s the geometry. The concentric rings don’t translate obviously into an even dice. If you cut an onion properly, then you leave the root end in tact (which you use as a handle to hold the rest of the onion while cutting it). Then you have a little end of onion leftover which can be saved with the rest of your veggie trimmings for broth. So without further ado: my treatise on slicing and dicing onions.
Before you start:
It is most important to use a very sharp knife. The tear-inducing chemicals are the product of a reaction that occurs when chemicals from different parts of the cell come into contact with each other. So the more you crush your onion’s cells with a dull knife, the more you will be crying.
1. Halve and skin the onion.
If you are preparing a lot of onions, then it can be worthwhile to soak them in tepid water for a few minutes. This will make the brittle skin more flexible and easier to peel off. If I’m just cutting one or two onions, I don’t bother. Cut the unpeeled onion in half from root to stem. Trim away the top quarter-inch of the onion, and then pull the peel away from the rest of the onion. Trim away the very edge of the onion roots; you only want to get rid of the roots that are holding dirt. Discard skin and root trimmings.
2. Make horizontal cuts.
With the palm of your left hand gently pressing down on the onion, make a series of three or four (depending on how big the onion is) evenly spaced horizontal cuts (the cuts should be about 1/4″-3/8″ apart). If you are right handed, that means the root end of the onion will be to the left and you will draw your knife from right to left, holding it parallel to the counter. Do not cut all the way through, though. Imagine a line about half an inch up from the root end and do not cut past that line. Keeping the root end in tact is the key to cutting onions efficiently.
3. Make vertical cuts.
For these cuts, the stem end of the onion should be facing you. Make a series of (6-7) evenly spaced vertical cuts. Again, leave the root end in tact by starting all of your cuts a half inch away from the root end. Place the knife blade precisely where you want the cut to begin (see illustration) and press straight down.
Hold the onion with your left hand, curling the tips of your fingers in (this technique makes cutting safer — your knuckles keep the knife edge away from the tips of your fingers.) It is a grip that feels awkward at first, but will actually allow you to cut more quickly once you have mastered it. Starting at the stem end, slice your onion in 1/4″-3/8″ slices (this is the exciting part, when all of your diligent skillful cuts reveal a gorgeous dice!). When you get down to the end of your onion, you will be left just holding the last little bit attached to the root end. Toss these onion ends in a freezer bag with the rest of your veggie scraps for making broth.
*If you want slices of onion rather than diced onion, skip steps 2 & 3.