Put butter, oil or combination in a large skillet over medium heat; when butter melts or oil is hot, cook carrot, onion, potato and thyme with a healthy sprinkling of salt and pepper. Stir occasionally, adjusting heat so vegetables do not brown. When onion is softened, about 5 minutes, add zucchini and continue to cook until everything is tender, 10 to 15 minutes.
Add pear and cook until it has softened, about 5 minutes more. Add liquid and bring to a boil; taste and adjust seasoning. Cool mixture, then puree. Serve cold or reheat and serve hot, garnished with mint, if desired.