Preheat oven to 350 degrees F. Wash the kale, dry thoroughly in a salad spinner or with paper towels, and tear into bite-size pieces. Toss in a large bowl with the olive oil and vinegar. Rub the kale to make sure each gets a coating of oil so they get crispy. Oil a baking sheet well!
Spread the kale in a single layer on the baking sheet. Sprinkle with kosher salt. Bake for 6 minutes, then stir and turn kale, and bake for 6-9 minutes longer. Remove crisp pieces as they are done to prevent burning (and allow remaining kale chips to get even heat. (Note: a single layer is important for crispy results). Eat while they are fresh if possible.