Before cutting your leeks, make sure to wash them properly to remove all the dirt. Remove any blemished or bruised leaves. If your leeks still have roots, cut away that area.   Thinly slice the leeks at about a 45-degree angle. The larger your pieces, the chunkier the filling will be and the longer it will take to soften. We prefer 1/8 – ¼ inch thick slices.