In a 2-quart saucepan cook carrot, onion, and celery in hot butter for 5 to 8 minutes or until tender, stirring occasionally. Add undrained tomatoes, vegetable juice, sugar, Italian seasoning, salt, and pepper. Bring to boiling; reduce heat. Simmer, uncovered, for 10 minutes. Remove from heat.
If desired, cool slightly. In a blender container or food processor bowl place half of the tomato mixture. Cover and blend or process until smooth. Repeat with remaining tomato mixture. Return all of the soup to the saucepan. Add enough water to reach desired consistency. Heat through.
To serve, ladle into bowls. Top with croutons and, if desired, sprinkle with Parmesan cheese. Makes 6 servings (about 4-1/2 cups).