Preheat oven to 450°F (For more crispiness, preheat your oven to 500°F.).
2 Peel the sweet potatoes and cut off the ends. Cut the potatoes in half lengthwise and then, if they are very long, in half crosswise. Cut each piece into wedges. Alternately, you can slice the peeled sweet potato into disks either with a mandoline or a sharp knife.
3 Put the sweet potatoes into a large bowl and add the oil. Mix well to combine. Sprinkle with salt, sugar and spices of your choice. Use your hands to mix well, so all pieces are coated with oil and spices.
Spread the sweet potatoes out in a single layer on a baking sheet; the oil they are coated with should keep them from sticking to the pan. If you are trying to cut fat, reduce the oil to 2 Tbsp and use a non-stick coating on the baking sheet. (Note: a commenter has recommended putting them on a wire cooling rack on top of a baking sheet, so that the oven air circulates around the sweet potato pieces and you don't have to turn them in the next step. Another commenter recommends preheating the baking sheet, to help the fries get crisp.).
5 Bake for a total of 25 to 30 minutes. After the first 15 minutes, remove the baking sheet from the oven and turn over all of the sweet potato pieces. Return to the oven and bake for another 10-15 minutes, or until they are well browned. Let cool for 5 minutes before serving.