Preheat oven to 425 degrees F. Line 2 large, rimmed baking sheets with lightly-oiled parchment paper.
Wash sweet potatoes and cut them into fry-shaped pieces about 1/4″ wide and 1/4″ thick. Try to cut them into similarly sized pieces so that fries will bake evenly.
Place fries in large bowl and sprinkle with cornstarch and salt. Toss until the fries are lightly coated in powder. Then drizzle the olive oil over the fries and toss until the fries are evenly coated in oil. If any powdery spots remain, use your fingers to rub visible cornstarch into the fries .
Arrange your fries in a single layer in each pan and don’t overcrowd, otherwise they will never crisp up. Bake for 20 minutes, then flip the fries so they can cook on all sides. Rotate pans and swap places on oven racks.
Bake for another 10 to 15 minutes, or until the fries are crispy. You’ll know they’re almost done when the surface of the fries change from shiny orange to a more matte, puffed-up texture. Keep a close eye on them.
Toss the baked fries with seasonings, to taste. Serve warm . If a dipping sauce is desired, see below.