How to Chop an Onion – into chunks

If you haven’t already, please make sure you’re familiar with basic knife safety before starting this tutorial. (link)

Onions are full of flavour, which gets sweeter the longer you cook them. The chunks we’ll be chopping today are perfect for long, slow, cooking that brings out all the best in onions.

Onions can be a little tricky to chop, because of their round shape and smooth skin. I would recommend using a serrated knife to chop onions; if you prefer to use a smooth knife I would start each cut by piercing the onion with the tip of your blade.

Hand drawing of a brown onion showing cutting guidelines (grey dotted lines)



Unlike carrots and potatoes, we don’t want to eat the skin of the onion. These dry, papery layers are best peeled off and discarded, and you can pull off any little rootlets from the bottom of the onion too. You might find that this is easier to do after you’ve started cutting the onion; as long as you take off the skin before cooking it doesn’t really matter!

The first two cuts are the trickiest – we want to chop the top and bottom off the onion. Make sure to hold the onion firmly on its side, but keep your fingers out the way!


Hand drawing of a red onion showing cutting guidelines (grey dotted lines)



You should now have a flat surface at the bottom of the ‘ball’, which you can rest the onion on to make the rest of the cutting safer. For these chunks, simply chop the onion in half straight down the middle. Cut each half in half again, then into quarters, and you’re done!




When you’re chopping or cooking onions, you might find that your eyes start to sting, burn, or well up. This is because sulphur-containing compounds that give onions a lot of their flavour can react with the water in your eyes to make sulphuric acid. If it becomes hard to see, it’s important that you don’t try and keep cooking – you’re likely to hurt yourself. You might find that washing your hands, knife or onion under clean water can help your eyes sting less; just make sure to pat everything dry before you go back to chopping.


These onion chunks are perfect for roasts, casseroles, and stews. They take about 2 hours to cook in an oven at Gas Mark 4 (180°C, 160°C in a fan oven). Once they’re cooked, onions become soft and the layers fall apart easily.

Photograph of roast onions with sausages on a brown plate
Roast onions are great with sausages!

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