Preheat the oven to 425°F and line two large, rimmed baking sheets with parchment paper.,

Cut both ends of the sweet potatoes to square them off. Then slice the sweet potatoes and cut each slice into thin even strips, about ¼” in thickness all around. Transfer to a large bowl.,

Sprinkle the cornstarch over the sweet potatoes and use your hands to toss together, making sure all the fries are well coated.,

Divide the sweet potato strips between the two baking sheets, and leave behind any excess cornstarch in the bowl. Drizzle the olive oil on top and season with salt and pepper. Use your hands again to toss the potatoes until there are no more visible streaks of cornstarch.,

Arrange the potatoes in a single layer, making sure not to overcrowd them. Bake for 20 minutes, then use a spatula to flip the fries and cook until they’re lightly browned and puffed, about 10-15 more minutes.,

Remove from heat, add additional salt, if desired, and serve immediately.