Preheat the oven to 450°. Start by slicing the potatoes into long ¼” to ½” thick batonnet cuts. Next, submerge them in water and let them sit for 30 minutes.
Drain the sweet potatoes and thoroughly dry them using a towel or paper towels. Add the potatoes to a large bowl and coat them in the oil on all sides.
Next, sprinkle in the corn starch and toss them until they are coated on all sides. Evenly spread the sweet potatoes on a sheet tray lined with parchment paper in a single layer.
Place on a middle rack in the oven and cook at 450° for 12 to 15 minutes or until they start to turn light brown. Flip the sweet potatoes over and cook for a further 6 to 8 minutes.