Melt the butter in a large pot and cook the vegetables until lightly browned. Pour in enough broth to cover vegetables and bring to a boil. Reduce heat to low, cover pot and simmer until all vegetables are tender, approximately 45 minutes.
Use either an immersion blender or transfer to a blender and blend until smooth. Return to pot and add either more broth or water to desired consistency. Season with salt and pepper and serve with a drizzle of good quality Olive Oil.