For this recipe I cut the leeks julienne. This is a French cooking term that basically means cutting them in to thin long slices - almost like matchsticks.
To do this with leeks, cut them in half lengthways and then lay them cut side down on a chopping board. Cut them thinly with a super-sharp large knife until you have small sticks. If your leek is very long then you probably want to cut it into around 3-inch lengths pieces first.
Place the sliced leek into a large bowl of cold water and then scoop it out to let any pieces of grit or dirt to dislodge and sink to the bottom.