Slice the sweet potatoes into sticks as evenly as possible, 1/4 to 1/2 inch wide and 3 inches long. Place them in a bowl of cold water and allow to soak for at least 30 minutes.
When ready to bake, preheat oven to 425 degrees Fahrenheit. Line a baking sheet with parchment paper and place in the oven to heat while you season the potatoes.
Lay the fries on a clean kitchen towel and blot dry. Place them in a large plastic zipper bag and add the cornstarch, shaking well to coat.
Mix the spices, salt, and pepper in a small bowl.
Carefully remove the baking sheet from the oven and place it on the stovetop. Spread the fries out in an even layer on the baking sheet, then drizzle with oil.
Sprinkle the seasoning mix on the fries and toss to make sure they are evenly coated.
Bake until brown and crisp on the bottom, about 15 minutes, then flip and cook until the other side is crisp, about 10 minutes. Serve hot.
Notes
These fries taste best when eaten immediately. If you do have leftovers, you can store in the refrigerator for up to 2 days and reheat in the oven or microwave.