Melt butter in large soup pot or Dutch oven, over medium heat
Add remaining ingredients. Bring to simmer. Cook, uncovered for 40 minutes, stirring occasionally.
Blend the soup and season to taste. Leaving the soup somewhat chunky is best. Blend the soup, and then season to taste. See notes for tips.
Notes
Using an immersion blender is best. If you do not have one, a regular blender is fine - allow the soup to cool slightly and blend it in batches to prevent a boil over.