Heat olive oil in a large pot over medium heat. Add onion and cook until softened, about 5 minutes.

Add garlic and cook for 1 minute more, until fragrant.

Add potatoes and vegetable broth to the pot. Bring to a boil, then reduce heat and simmer for 20-25 minutes, or until potatoes are tender.

Carefully transfer the soup to a blender (or use an immersion blender) and blend until smooth.

Return the soup to the pot. Stir in butter and heavy cream (if using). Season with salt and pepper to taste.

Garnish with chopped chives and serve hot.