Preheat oven to 375 degrees F and place oven rack in the center of the oven.
Thinly slice beets with a mandolin (or a sharp knife), getting them as consistently thin as possible. They should curl a little when cut. This will ensure even baking and crispiness.
Divide between two baking sheets and spray or very lightly drizzle with olive oil. Add a pinch of salt and the rosemary. Toss to coat, then arrange in a single layer, making sure the slices aren’t touching.
Bake for 15-20 minutes or until crispy and slightly brown. Be sure to watch closely past the 15 minute mark as they can burn quickly.
