Preparation In a 6-quart kettle bring water with ham hock to a boil (water will not cover hock) and simmer, covered, turning hock over halfway through cooking, 1 hour. While hock is simmering, remove and discard stems and center ribs of collard greens and cut leaves into 1-inch pieces. Stir collards into hock mixture and simmer, partially covered, until almost tender, about 45 minutes. Cut turnips into 1/2-inch cubes. Stir turnips into collards and simmer, partially covered, until turnips are tender, 12 to 15 minutes. Season collard and turnip mixture with salt and pepper. Collards and turnips may be cooked 8 hours ahead and cooled completely before being chilled, covered. Reheat collards and turnips before serving. Serve collards and turnips with pepper vinegar.