Wash and scrub the potatoes thoroughly. Peel, if desired. I prefer the skins on. Slice each potato in 4-5 vertical slices, about 1/4-1/2 inch thick. Cut each slice into 1/4-1/2 inch matchsticks. Place into a large bowl and cover with cold water. Let sit for 45 minutes.
Drain and rinse potatoes. Spread out on paper towels and dry very thoroughly.
Preheat oven to 375. Spread 1 tbsp oil in the bottom of 2 rimmed baking sheets and place into warming oven, staggered on lowest 2 racks.
In a large bowl, whisk together 2 tbsp oil, 1 tbsp cornstarch, and 1 tsp salt. Toss dried potatoes in mixture until evenly coated.
Carefully slide out oven racks with baking sheets and spread potatoes into a single layer on each of the hot pans. Bake for 20 minutes.
Flip fries, return to oven and increase oven temperature to 450. Bake for 20-25 more minutes, or until golden brown and crisp.