Place an onion or shallot on its side.
Cut off the base (about ½ cm or ¼") and discard.
Do the same with the top.
Slit the whole height of the skin down the side.
Peel off the skin to leave just the white flesh.
Rinse and dry.
Cut in half lengthways.
Place flat side down, and slice horizontally, but without cutting right to the end, so that the slices are still held together.
Then slice vertically, again without cutting right to the end. You will then have small sticks held together by the uncut portion.
And finally, slice downwards, as if slicing the half shallot normally, to cut into small pieces ready to add to your recipe.
Finish by chopping the uncut portion.
Do the same with the other half, and your shallot is ready for use.
See all this steps in a small video.