Sweet potato fries are harder to get crispier in the oven than regular potatoes. First, you want to cut your fries into pretty thin pieces, about 1/4 inch in thickness. The thicker the fries, the less crispy they will become! To keep them crispy, I like to place them in a single layer on a baking sheet. Make sure not to overcrowd them or else they will steam and not crisp up! It is important to add the cornstarch in this recipe, too. This will do the trick to really crisp up the fries in the oven!