Slice each leek in half lengthwise, then slice each half into 1/2" think half moons. ( approx. 2 cups). Place in a large bowl of cold water swish to remove any grit. Drain and pat dry. Remove the stems from the kale. Stack the leaves on top of one another and slice them crosswise into 1/2" wide strips, you'll need 3 cups. Heat the oil in a saucepan over medium heat. ( I use a 6 quart pot). Add the leeks and cook for 3 minutes. Add the tomatoes and cook, breaking them up with a spoon for 5 minutes. Add the water and bring to a boil. Stir in the kale, sweet potatoes, lentils thyme, salt, pepper and basil. Simmer until the lentils are tender, about 30 minutes. Spoon into individual bowls. Sprinkle with the parmesan. Makes about 6 servings.