Preheat the oven to 425 degrees. Line a large baking sheet with parchment paper.
In a large bowl, combine the sweet potatoes and cornstarch. Toss to coat.
In a small bowl, whisk the maple syrup, miso and vinegar to blend. Pour the mixture over the sweet potatoes and toss them to coat. Spread the sweet potatoes on the prepared baking sheet in a single layer.
Bake for 25-30 minutes, flipping the fries at the halfway point or until lightly browned. Season with salt and pepper.