Peel and slice sweet potatoes into fry-sized sticks. Preheat oven to 425* F and grease a large baking sheet.
Pour buttermilk into a medium bowl. In another bowl, mix bread crumbs, cinnamon, and sugar. Working in batches, coat sweet potato fries first in buttermilk, then in bread crumb mixture. Place on baking sheet.
Bake for 20-25 minutes, until the potatoes are soft inside and golden brown on the outside.