Preheat the oven to 425°. Line 2 large baking sheets with parchment paper.
Peel the sweet potatoes and cut them into fry-shaped pieces about 1/3" wide and 1/3" thick. *It's better for these to be a little thicker rather than super thin. They will take a little longer to cook, but they won't dry out and burn and it will give the cornstarch more time to soak in and cook.*
Dump the fries into a large bowl and add cornstarch (use 1 tsp per pan), salt (1/4 tsp per pan), and any other seasonings.
Toss until all the fries are lightly coated in powder.
Drizzle the olive oil over the fries (1 1/2 Tbsp per pan) and toss until the fries are evenly coated in oil and no powdery spots remain (use your fingers to rub visible cornstarch into the fries as necessary). *You want more oil and less starch ratio - in other words, the fries should look greasy and there should be no evidence of cornstarch. This give the cornstarch enough moisture to soak up.*
Arrange the fries in a single layer on the pans, making sure to not overcrowd - otherwise they will never crisp up.
Bake for 20 minutes, then flip the fries so they can cook on all sides.
Bake for 10-18 more 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 an eye on them, as they can turn from crisp to burnt quickly.*