How can I easily separate onion layers in diced chunks?

Question

I often want a small portion of onion in the form of short pieces, one layer thick. I start by cutting a slice from the onion that is about the total amount needed.

While it's a slice, the rings can be easily separated, but that makes it more difficult to cut it up. So I keep the slice intact, and cut it into horizontal and vertical strips, creating rectangular chunks. The chunks typically contain several layers, and those are difficult to separate.

Is there any trick to easily separate the layers in the diced pieces (or a better cutting method to reach the same result)?

I'm just working with a sharp knife. There are probably cutters or choppers designed to make this easy, but I'd rather not buy another kitchen tool.

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Addendum: I appreciate all the suggestions, and tested them all. I'll add comments under the answers with the results so people can compare them.

Answer 1

When cutting the onion, after you’ve halved it and cut along one dimension, smoosh it down a bit with the palm of your hand. This will cause the layers to shear against each other, loosening them. Then finish chopping them.

If there are still big chunks, put the pieces in a closed, hard-sided food storage container and give it a few good shakes. (Don’t overdo this, as overly bruising onions will lead to that unpleasant stored-raw-onion smell.)

Answer 2

Put the chopped onion into a bowl of cold water to soak for a few minutes. This will loosen the sticky membranes between the layers, and they should come apart easily with just a little stirring and rubbing with your fingers.

Soaking raw onion is also commonly practiced to reduce the sharp flavor of the onion by diluting and halting the enzymatic reaction that produces the sulfur-rich compounds. The sweet and complex flavors of the onion remain, but with less "hotness", and the texture is not significantly changed.

Answer 3

Rub them between your palms. It's imperfect, as it won't get every single one, but it will get the majority.

I can't think of a better method to work on a single slice. There's a good method to work on a whole or even half onion, but it still doesn't necessarily separate each individual layer; it relies on cooking to complete that.

Answer 4

There are plenty of 'hacks' for cutting even, diced onions

1. Don't chop off the root
2. Follow the lines of the onion
3. Keep your fingers tucked under

Check this video https://youtu.be/v17DxxrETAQ?t=42

But if you can afford it I would highly recommend getting a Cuisinart food processor

https://www.cuisinart.com/shopping/appliances/food_processors/dfp-14bcny/

This has been an absolute game changer, it can knead dough, blend vegetables in to ultra smooth soup and dice onions in seconds. It takes a bit of getting used to, the first time I tried dicing an onion it turned into liquid. But once you're used to it, it is incredible.

I just remove the onion peel and roots, chop the onion into quarters and the cuisinart does the rest. Onions come out perfectly diced, all equal sizes.

An interesting thing I've noticed is that when I fry onions processed this way they will caramelize almost instantly. Perhaps due to how evenly sliced they are.