Hold the onion with one hand, and keep the sharp edge of the knife away from that hand. Push the tip of the blade into the leek and slide the knife down the length of the leek to slice it.
When the knife reaches the end of the leek, flip it over and slice it again, until the leek is sliced into several strands.
Finally, cut the leek across the strands to mince them.
Story Behind this Recipe
I used to use a method of diagonally slicing the leek and then mincing from there, but...for some reason that was pretty difficult for me. (lol). So I thought, wouldn't it be easiest to just push the knife into the leek to make the cuts? And when I tried it, it was so easy! I uploaded this so that I could teach to my kids.
Please absolutely make sure to hold the edge of the blade away from your other hand! It's dangerous. A knife with a small blade will probably be easier to handle. You can mince the leek into any size that you want.