How to Make It
Preheat oven to 425°F with racks in upper third and lower third positions. Toss together sweet potatoes and cornstarch in a large bowl until evenly coated. Drizzle with oil; toss until evenly coated. Arrange in a single layer and evenly spaced among 2 baking sheets lined with parchment paper. Bake in preheated oven until bottoms start to brown, about 15 minutes.
Remove from oven. Flip fries using tongs, moving smaller fries toward center of baking sheet if browning too quickly. Return to oven, rotating sheets between top and bottom racks. Bake at 425°F until browned and crisp, 10 to 15 minutes. Remove from oven. Sprinkle fries evenly with salt. Serve immediately.