Melt butter in a large stock pot over medium heat. Stir in leeks and carrots. Cover pot, turn heat to low and let vegetables sweat for 20 minutes. Meanwhile, bring a pot of water to boil, add the kale and let boil for 8 minutes (this helps reduce the goitrogens in the kale). Drain.
Add the chicken stock, wine (if using), crushed tomatoes, and lentils to the carrot mixture. Bring to a boil and then lower heat and simmer for about 45 minutes or until lentils are soft. Using a ladle transfer about 4 cups of soup into a blender and blend until smooth. Pour pureed soup back into pot. Stir in cooked kale and lemon juice. Season soup with salt and pepper if needed. Serve soup with a dollop of crème fraiche and a sprig of dill.