Add the lentils, water or broth, and bay leaf. Bring to a boil, then turn the heat down to low and let it simmer until the lentils begin to fall apart and become creamy. Add more water or stock if needed. The lentils will thicken as they cook about 25-30 minutes. Stir soup often so it does not stick to the bottom of the pot. Alternatively remove the bay leaf, blend the soup in a blender or use an immersion blender until smooth and creamy. Serve hot.