Preheat 300 degrees. Cut kale into 2 to 3 inch pieces. Combine vinegar, oil, salt, in a large bowl; add kale and toss by hand to coat leaves. Place and layer on baking sheet (use parchment paper for easy cleaning) and bake until crispy- about 20 minutes. They should be sizzling and crispy, if not turn up to 400 degrees. But be careful. They can burn easily.