Tough greens, like kale and collard greens, can take some work to make them suitable for salad, but if you marinate them in oil for a bit first you'll tenderise them, make your salad even tastier and start a light dressing all at the same time.
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The waxy coating on greens like kale is oil soluble, which is why a quick bath in the oil you'll use for your dressing is able to break through and tenderise the leaves. When prepping your greens, massage them with a little oil, then let them sit for about half an hour. Drain extra oil, pat them dry a bit if you want to get even more off and finally add some acid or other dressing ingredients and toss the greens. At the end,you'll have a salad with a more enjoyable texture. If you're concerned about added fat or kilojoules from the oil, just account for it when mixing your dressing, and you'll be all set.