Broccoli and Cheese Soup

Melt butter in a large saucepan over medium heat. Add onion and garlic and cook until translucent, about 5 minutes.Add broccoli, potato and chicken broth. Raise heat to high and allow to boil. Reduce heat, cover and simmer until the broccoli and potato soften, about 7 minutes. Let broccoli mixture cool slightly, then transfer to a blender or food processor. Pureé until smooth.Return soup to saucepan, add buttermilk and 1/4 cup cheese. Cook soup over low heat until cheese melts (do not allow it to boil), about 3 minutes. Season with salt and pepper to taste. Pour soup into bowls and top each with remaining cheese.