Preheat the oven to 425 degrees F. Line a baking sheet with parchment paper or foil and set aside.
Peel the sweet potatoes and cut them into fries with either a sharp knife, a mandolin, or a fry cutter. Place the fries in a gallon-sized bag and drizzle in the olive oil. Seal the bag and give it a shake to coat all of the fries in the oil.
Add in the cornstarch, chili powder, pepper, salt, and cayenne pepper if using. Give the bag another shake and then transfer the fries to the prepared baking sheet. Try to make sure the fries aren't stacked on top of each other, so put them all in an even layer. (You may need two pans.)
Sprinkle with extra salt if desired and place the pan in the oven for 25-30 minutes, flipping the fries about half through the cooking time.
Take them out of the oven and let them cool for about 5 minutes before eating. Not only will this keep you from burning your taste buds into oblivion, but it will also give the fries another chance to crisp up.
Serve with ketchup, or by themselves!
Recipe by Natural Chow at http://naturalchow.com/2015/03/baked-sweet-potato-fries/