Begin by rinsing and peeling the sweet potatoes thoroughly.
Cut each potato into rectangular slices, about 1/4 inch thick. Then, slice across to achieve the classic fry shape, also 1/4 inch thick. I prefer them thin, but you can adjust the thickness to your liking.
Place the slices in a bowl of ice water and let them soak for 30 minutes.
Drain the ice water and rinse the potatoes 2 to 3 times, shaking them well to remove excess starch.
Bring a pot of water to a boil and add the potatoes. Boil for just 3 to 5 minutes; they should not be too soft.
Pat the fries completely dry and place them in a tray or large bowl. Sprinkle with cornstarch and shake to coat evenly.
In a small bowl, mix cornstarch and club soda to make the batter.
Heat oil in a frying pan over medium-low heat until it reaches about 250°F. The oil shouldn't be too hot for the first fry.
Add the French fries and flash fry for 4 to 6 minutes. They won't turn golden yet, but they'll hold their shape.
Fry in batches to avoid overcrowding the pan.
Increase the oil temperature to about 350°F. Fry the fries again until golden and crispy, ensuring they brown evenly.
Transfer to a wire rack to drain excess oil. Sprinkle with salt.
Enjoy your crispy sweet potato fries with ketchup or your favorite dipping sauce!