Place rack in the upper ⅓ of the oven. If using 2 racks place one in the upper ⅓ and one in the lower ⅓.
Mix the cornstarch and salt. Set aside.
Mix the brown sugar and remaining spices. Set aside.
Preheat the oven to 425F.
Oil baking sheets lightly with oil.
Peel the sweet potatoes and cut them into fries about ¼-inch wide by ¼-inch thick. Make them as evenly sized as possible.
Toss into the cornstarch and salt mixture to coat evenly - shaking off excess.
Oven Instructions
Place half on each baking sheet, in a single layer, being careful not to overcrowd.
Drizzle oil over the fries and toss to coat with oil.
Bake for 20 minutes.
Remove the pans from the oven and carefully flip the fries so the other side can get crisp.
Bake for 15 more minutes, or until they are crispy.
Watch carefully - they'll burn pretty quickly.
Remove from oven and season with the seasoning mixture.
Let stand for 5 minutes.
Serve hot.
Air Fryer Instructions
Arrange about half of the uncooked sweet potato fries in a single layer in an air fryer basket - make sure there is plenty of room between them.
Air fry at 375F for 8 minutes.
Flip and air fry for 8 more minutes.
Remove from air fryer and sprinkle with seasoning.
Repeat with remaining sweet potato fries.
Notes
It's been said but it bears repeating - be sure to cut the fries in thin, even pieces- about ¼-inch thick.
Sweet potato fries can be cut a day or two ahead of time and stored in the refrigerator until you're ready to bake. If you keep them in a bowl of water with a little squeeze of lemon in it they won't discolor. Just be sure to pat them very dry before finishing the recipe.
Always flip the fries about halfway through.
Don't crowd them or they will steam rather than oven-fry.
Let sweet potato fries rest for around 5 minutes after they come out of the oven to crisp up even more.
Don't let them sit too long or they will get soggy.
They are best when they come right out of the oven but you can warm up leftovers in the oven until they crisp back up.