An organ meat, beef kidneys are large and tough and require a long cooking time. They also must be cleaned before cooking. Traditionally prepared in a stew, start by removing as much of the fat and sinews as possible. Cut each one in half, and cook 2-3 minutes in simmering water. Drain the water and rest the kidneys for up to an hour before continuing to cook in a stew with pancetta, onions, garlic, wine and other vegetables.