
Preheat oven to 450 degrees with racks in the upper and middle positions. Line two baking sheets with parchment paper and rub with oil.
Prepare the Buffalo Dipping Sauce: Whisk melted butter, sriracha sauce, tabasco sauce, vinegar & ketchup together in a bowl. Set aside.
Prepare the fries: Put sweet potatoes in a microwave-safe container, cover, and microwave 2 minutes. Stir gently, cover, and microwave 1 to 2 minutes more until pieces are pliable. Let rest 5 minutes covered; pour onto a platter to cool.
In a large bowl, whisk egg whites until frothy, add salt and rosemary, and whisk to blend. Working in batches, toss the sweet-potato pieces in the seasoned egg whites, letting the excess liquid drip back into the bowl. Place in a single layer on prepared baking sheets. Bake 10 minutes, then flip pieces over with a spatula. Rotate baking sheets from front to back and from one rack to the other. Bake until dark golden brown, about 15 minutes. Serve immediately with the Hot Buffalo Dipping Sauce on the side.
