How to make sweet potato fries: Preheat oven to 400F and grease a baking sheet. Cut the potatoes into fry shapes (thick or thin), then soak them in water for around 45 minutes. This is the important step to make them crispy! Drain, and pat dry. Toss the fries with the oil or oil spray in a large bowl. Add all other ingredients and mix well. Spread the fries on the baking sheet. Bake 25-30 minutes, turning halfway through. For even crispier fries, feel free to leave them in longer or broil for the last 1-2 minutes. A reader also left the advice to cook them on parchment paper, which will absorb some of the moisture.