Carefully tuck 6 apple slices between the leaves in each endive half. In a large skillet, melt the butter in the oil over high heat. Add the endives, cut sides down, and cook over moderate heat until nicely browned, about 6 minutes. Carefully turn the endives. Season with salt and pepper and add the water to the skillet. Cover and simmer over low heat until the endives are tender, 12 to 15 minutes. Uncover and cook until the liquid has evaporated. Serve hot.