In a Dutch oven or large heavy saucepan, melt the butter over medium heat; add the celery and onion and cook until the celery is tender, 7 to 10 minutes. Add the tomatoes, basil, oregano, thyme, parsley, bay leaves, and stock and bring to the boil. Simmer about 30 minutes. Remove from the heat and remove the bay leaves. Puree the soup in batches in a blender or food processor, leaving the soup slightly chunky. Season to taste with sugar, salt, and pepper. Serve hot. Garnish with shaved Parmesan if desired.