Preheat the oven to 300 F. Line two large baking sheets with parchment paper or silicone baking mats.
Wash and dry the kale thoroughly. Remove the hard stems from the kale, and tear the remaining leaves into 1- to 2-inch pieces.
Using your hands, massage the kale, olive oil, apple cider vinegar, and salt together in a bowl for 1 to 2 minutes, or until slightly softened.
Spread the kale across the two baking sheets, and cook for 18 to 22 minutes, or until the edges begin to turn brown and the center stays green. Remove from the oven, and serve.