Heat the oven to 300°F. Pull the kale leaves from the stem; discard the stem. Tear the leaves into 3-inch pieces (8 to 10 cups total) and place on a rimmed sheet pan. Toss with the oil and rub to evenly coat each leaf. Arrange in a single layer and bake until crisp, 20 to 25 minutes. Let cool, then sprinkle with salt and Parmesan to taste before serving.