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How to Slice and Dice an Onion

Learn how to cut an onion into uniformly-shaped pieces so it cooks evenly

Sarah Breckenridge
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In this video, our Test Kitchen expert shows one method for slicing onions, and another for dicing onions, so you get quick consistent results every time.More recipes than you can count start with a little sliced or diced onion, so it’s important to learn the right way to cut an onion into uniform-sized pieces. Why do they need to be the same size? If there’s too much variation in size, some pieces can start to burn before others even soften. In this video, I’ll show you one method for slicing onions, and another for dicing so you get quick consistent results every time.

The most intuitive way to slice an onion is to cut it in half, and then make horizontal slices from the stem end to the root end. This is fine if you’re using the onion raw, like for a salad. But you’ll end up with some really big half moons and some really small half moons. And if you’re cooking them, that means the varying sizes will cook unevenly.

So instead, you’ll want to make what are called radial cuts. That means you’re cutting slices from pole to pole, rather than across the equator.
To do that, you trim both ends, and cut out a notch at the top. Then start making thin slices, following the curve of the onion. When you get to the top, it can get a little wobbly, so flip the onion onto this side and finish the rest.

It can feel a little awkward the first couple times you do it, but soon it gets to be as natural as slicing crosswise. And your half moons will be mostly same length, which means when you cook them or caramelize them, each piece cooks at the same rate.

If your recipe calls for diced onions, again, the key is to get all the pieces the same size, so they cook at the same rate. The best way to do that is again cut the onion in half through the stem and the root and peel it—then trim off the stem, and the hairy part of the root, but leave this button at the base of the root intact. Now make a bunch of vertical cuts through all the onion layers, but don’t go all the way to the root end, you want the root to hold everything together while you dice.

Depending on how large of a dice you need, these cuts can be close together, or farther apart—the important thing is keep them consistent.

The next part is slightly tricky: Go in horizontally and make several cuts the same size. If it helps, you can stand the onion up on its root end.

Then finally, you come back through with a bunch of crosscuts to release all the dice—and there you go. You have a nice, even dice that is perfect starting point for sautés, soups, or a million other dishes calling for diced onion. 


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