Leeks often contain sand between their many layers. Cut the leeks lengthwise in half. Rinse under cold running water, gently separating the leaves to allow the water to flush out any trapped sand or dirt.
Once peeled, parsnips may turn dark when exposed to air, so be sure to roast them right after they're chopped. If you want to get a head start on prep, store peeled and chopped parsnips in acidulated water (just add a bit of lemon or lime juice or vinegar to water).—Sara Petrie, Grassie, Ontario