The optimal oil for frying delicate vegetables quickly is a high smoke point oil that can result in an ultra-high temperature. It's the only way that you're going to cook something as moisture-packed and delicate as leeks crispy. Even without the coating recommended, tossing in the thinnest leek fries possible will still come out crunchy on the outside with little oil absorption if you use refined avocado, refined peanut, refined canola, refined safflower, palm or grapeseed oil.