I Loooove Sweet Potato fries. Who doesn't? But I don't like the fact that they often come out limp and mushy when they're baked in the oven, and I don't like all the fat and calories that deep frying them, or even using oil when you bake them imparts. What to do?
Well, after some experimentation, and internet sleuthing, I think I've finally hit upon the solution. The key is water. You need to remove as much of it as possible from the potatoes and the baking process in order to ensure crispy fries. Sweet potatoes are starchy, and while this makes them sweet, it also allows the starch molecules to retain moisture, so the first step is to get as much starch out of them as possible. Ironically, you do this by soaking them in cold water for a couple of hours. Next, I used egg whites and corn starch to give them a crispy coating, without adding additional fat from oil (also, the oil seals in moisture which we don't want). And finally, I baked them in a super hot oven, on parchment paper instead of foil or a silicon pad, which tends to let things steam as well. —Burnt Offerings
Wash the sweet potato and cut it into 1/2 inch batons or fries. You don't have to peel it.
Fill a bowl with the water, and place the fries in the water for anywhere from 1- 12 hours. You can also leave them in the fridge all day while you're at work and make them for dinner. I often cut one up at breakfast, soak it, and have it later for lunch.
Heat the oven to 450' and line a baking sheet with parchment paper.
Rinse the fries thoroughly in cold, running water, and dry thoroughly on paper towels. Get them as dry as you can.
In a small bowl, whisk together the corn starch, salt and spices. In another small bowl, whisk an egg white until very frothy, but still in liquid form.
Using tongs, toss the fries in 1/2 of the spice and cornstarch mixture, and then pour over the egg white, and toss again to thoroughly coat the fries in egg white. Finally, add the remainder of the corn starch and spice mixture and mix one more time to make sure everything is coated well.
Place the fries on the parchment paper and give them room to breathe - don't crowd them. If you're making a double batch, use two sheets and rotate the pans.
Place in the bottom third of the pre heated oven, and bake for 20 minutes, turning the fries and rotating the pan halfway through. It's also not a bad idea to open the oven every five minutes to let any moisture escape.
Serve with chipotle mayo, mayo with Siracha sauce, or cilantro and lime aoli. Even BBQ sauce makes a great dip.