Heat oven to 425°F. Finely grate sweet potatoes into a bowl. Squeeze grated sweet potatoes in batches to release as much moisture as possible and place in another bowl; fluff with a fork. Stir in cheese, egg whites, rosemary and pepper. Line a large cookie sheet with parchment paper. Spoon 1 rounded tablespoon batter onto cookie sheet and flatten into a thin, 2- to 2 1/2-inch round. Repeat with remaining batter, leaving 1 inch between rounds.
Bake until edges and underside are crisp and browned, 13 to 15 minutes.
Remove from oven, let cool slightly and remove from parchment.
