Preheat the oven to 400 degrees Fahrenheit. Line two cookie sheets with a silicone baking mat (such as SILPAT) or foil, lightly sprayed.
Cut the sweet potato into half, then into quarters, then cut into even fries (not too thin). In a plastic ziplock bag, add the fries and the cornstarch and shake until all the fries are coated, for about 1 minute.
Add the oil to the bag and shake again, coating all of the fries. Add all the seasonings in a ramekin, and then add the bag and shake again to coat fries.
Pour the fries onto the baking sheets so that they are NOT crowded (very important or they will just steam each other and not crisp) and slightly spread out.
Bake for 23-25 minutes, watching them after 20 minutes so they don't burn. Remove from oven once done and serve hot with mayo and ketchup. Enjoy!