Cut stems and center ribs away from kale leaves and coarsely tear leaves. In a large heavy saucepan of boiling salted water cook leaves 5 minutes and drain well in colander. In pan cook bacon over moderate heat, stirring, intil crisp. Pour off all but about 1 tablespoon fat from pan. Add kale to bacon and sauté over moderately high heat, stirring, until heated through. Toss kale with vinegar and season with salt and pepper.
