1 tablespoon butter
1/2 medium onion, chopped
1 clove garlic, minced
2 cups broccoli florets
1 medium Yukon Gold potato, peeled and diced
2 1/2 cups low-sodium chicken broth
3/4 cup buttermilk
1/2 cup shredded cheddar cheese
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.