Using the flat side of a large knife, crush the cardamom pods to release the seeds. Transfer the seeds to a pestle and mortar and crush them finely: you should have about ½ teaspoon. The pods can be discarded. If starting with ground cardamom you don’t need to do this.
Mix a pinch of cardamom (about ⅛ teaspoon) with a pinch of salt. Rub this on both sides of the f