1. Heat the olive oil in a saucepan over low heat. Add the carrot, celery, onion and thyme, season lightly with pepper and cook for 10 minutes. (Do not add salt until the lentils are fully cooked, because salt will prevent the lentils from becoming tender.)
2. Add the stock and lentils and bring to a boil quickly over high heat.
3. Lower the heat and simmer until the lentils are tender, about 1 hour.
4. Puree 2/3 of the soup in a blender and stir it into the remaining 1/3.
5. If the soup is too thick, thin it by adding a little more stock. Raise the heat and bring the soup to a boil for 15 seconds.
6. Add salt and more pepper to taste.
Serving Size: 1 1/4 cups