Peel your sweet potatoes and then slice them evenly into thin slices (about 1-3 - 1/4 of an inch, depending on how thin or thick you want them to be).
Soak the slices into a bowl of ice cold water for a minimum of 30 minutes and a maximum of 8 hours. This allows the starch to separate from the fries and allows for crispiness.
Preheat oven to 220°c. Prepare the oven tray with a baking paper and lightly brush with some oil.
Drain the fries from the water, pat with a paper towel until they are completely dry and then put them in a dry bowl.
In a separate bowl mix the oil, spices (not the salt just yet)and cornstarch. Make sure to whisk the cornstarch in by adding it bit by bit to avoid lumps from forming.
Evenly spread the fries into the baking tray. Make sure there is not much overlap, this allows for maximum crunchiness.
Bake for 15 minutes. Then flip over the fries gently with a spatula and bake for another 15 minutes. You will know the fries are ready when the tips of the fries turn dark brown.
Allow to cool for 5-7 minutes on a cooling rack and sprinkle with salt. Enjoy them warm.