Cut away inner ribs from each kale leaf and discard; tear the leaves into pieces of uniform size. (I made my pieces about the size of a small potato chip.) Wash torn kale pieces and spin dry in a salad spinner or dry with paper towels until they're very dry.
Put the kale pieces into a large resealable bag (or use a bowl if you don't mind getting your hands oily). Add about half the olive oil; seal and squeeze the bag so the oil gets distributed evenly on the kale pieces. Add the remaining oil and squeeze the bag more, until all kale pieces are evenly coated with oil and slightly 'massaged.' Sprinkle the vinegar over the kale leaves, reseal the bag, and shake to spread the vinegar evenly over the leaves. Spread the leaves evenly onto a baking sheet.
Roast in the preheated oven until mostly crisp, about 35 minutes. Season with salt and serve immediately.
