Preheat the oven to 425 degrees. Line a large rimmed baking sheet with parchment paper or aluminum foil and then set aside.
In a shallow bowl, stir together the flour, salt, and pepper. In a separate shallow bowl, lightly beat the egg whites with 2 tablespoons of water until combined. Place the Parmesan on a sheet of waxed paper or put it in another shallow bowl.
Dip the sweet potato first in the flour mixture, shaking off excess. Then dip each wedge into the egg white mixture until coated. Finally, dip the sweet potato in the Parmesan, pressing the exposed surface of the potato into the cheese. (Don't worry if some gets on the skin.) Transfer potato wedges onto the prepared baking sheet as you go.
Bake potatoes until tender and crisp, about 25 minutes. Serve sprinkled with more salt if desired.