Preheat your oven to 425°F (220°C) and position racks in the lower and upper thirds of the oven. Ensure the top rack is no closer than 6 inches from the heat source. Line two large, rimmed baking sheets with parchment paper to prevent the fries from sticking.

Peel the sweet potatoes and slice them into fry-shaped pieces, each roughly ¼ inch wide and thick. Ensure the fries are similar in size for even baking. Distribute half of the cut fries onto each prepared baking sheet.

Evenly sprinkle cornstarch over the sweet potato fries (about 1 ½ teaspoons per baking sheet) and add sea salt (¼ teaspoon per sheet). Toss the fries until they are uniformly coated in the cornstarch. Drizzle with olive oil (1 tablespoon per sheet) and toss again, ensuring no powdery spots remain. Use your fingers to rub in any visible cornstarch, if needed.

Arrange the fries in a single, even layer, making sure they are not overcrowded to promote crispiness. Bake for 20 minutes, then flip the fries to ensure they cook evenly on all sides. Use a metal spatula to flip them in sections, turning about ten fries at a time with a swift flick of the wrist.

Reorganize the fries into even layers on the baking sheets, shifting any overly browned fries toward the middle of the pan to prevent overcooking. Return the sheets to the oven, swapping their positions so the former top pan is now on the lower rack, and vice versa.

Continue baking for an additional 10 to 18 minutes, or until the fries achieve a crispy texture. Look for a change from a shiny orange to a more matte finish with puffed-up surfaces. Monitor closely, as fries can quickly go from crisp to burnt. The batch on the lower rack may finish a few minutes before the one on top. Slight browning at the edges is fine—it will add a caramelized flavor rather than a burnt taste.

Once baked, season the fries with additional spices to your preference. Consider adding freshly ground black pepper, a scant ¼ teaspoon of cayenne pepper, or a dash of garlic powder. Serve the fries warm.