I’ve used a red onion here for contrast (and because it’s what I was using that particular day) but any sort is fine.
First, cut your onion from root to tip. If you open it up and see concentric circles, you’ve done it the other way and the rest of this method won’t really work for you, sorry :)
Now, here’s where it gets good. Peel off the skin including one layer of “good” onion. This means you’re not fussing with loads of papery skin flaking all over your kitchen. Yes, it’s a bit of a waste and my mother is rolling her eyes right now, but in the interests of my sanity I choose to waste a little onion.
Now trim both ends off neatly, leaving a little of the root part (indicated by the arrow). This holds all your layers together nicely while you chop and means you don’t have to chase chunks of onion all over your board. Ask me how I discovered this.
Now slice the onions in parallel slices (the width will depend on how fine you want it – I have done fine on the top and coarser on the bottom), but do not slice all the way through at the root end. Finish each cut a little short of the root end, leaving the root itself intact. This holds your onion together. You’ll want to prepare all of your onions up to this point.
Now you’ll slice perpendicular to your first cuts, making approximate squares. Again, finish a little short of the root end.
This is what you’ll end up with. You can then chop around the root any old way you like to minimize wastage. You’ll then be left with:
This, to go in your compost, and....