2 pounds sweet potatoes (about 2 medium-large or 3 medium)
2 teaspoons of arrowroot or 2 tablespoons of cornstarch
½ teaspoon fine sea salt
2 tablespoons extra-virgin olive oil
Optional spices: freshly ground black pepper, garlic powder
Directions
Heat oven to 425°F with racks in the lower and upper thirds. Keep the top rack about 6″ from the heat source, no closer. Line two large, rimmed baking sheets with parchment paper.
Peel the sweet potatoes and cut into even fries about ¼″ wide and ¼″ thick. Divide between the baking sheets.
Toss each pan of fries with 1 ½ teaspoons cornstarch and ¼ teaspoon salt until lightly coated. Add 1 tablespoon olive oil per pan and toss until evenly coated, rubbing in any powdery spots.
Spread in a single layer without crowding. Bake for 20 minutes, then flip with a metal spatula, working in small sections.
Spread the fries evenly again and move browned pieces toward the center. Return the pans to the oven, swapping the upper and lower positions.
Bake for 10 to 18 more minutes, until crisp. Look for a matte, puffed surface rather than shiny orange. Watch closely to prevent burning; the lower pan may finish first. Lightly browned edges are fine.
Season to taste and serve warm. Optional: freshly ground black pepper and a scant ¼ teaspoon each cayenne pepper and garlic powder.