The best way to cook black lentils is to sort them when they are dry by removing any debris and small pebbles. Then place in a medium saucepan and cover generously with water. Do not salt the water or the lentils will become tough. Place the pot over high heat and bring to a simmer. Reduce the heat to maintain the gentle simmer, then cook until they are just tender, about 22 minutes. Drain well.