Preheat oven to 425. Set a wire rack on top of a baking sheet. Spray rack with non-stick spray. Peel the sweet potatoes. Grate sweet potatoes and then squeeze the moisture from them. The more moisture you remove, the crispier they will get in the oven. To the grated sweet potatoes, add the egg whites, cheese, pepper, and rosemary. Mix until combined. Scoop out potato mixture and set on wire rack. (You can use an ice cream scoop.)
Press sweet potato mixture as thin as possible. Bake for 25-30 minutes or until potatoes are crispy and dark around the edges.