Melt butter in a large saucepan over medium heat. Add the leek, garlic and potatoes, season with salt, cover with a tight-fitting lid and cook for 4 minutes or until softened.
Add stock, milk and white pepper and cook, covered, for 10 minutes or until the potato has softened. Remove from the heat, add the parmesan and, using a stick blender, blend until smooth.
Divide soup between bowls, top with burrata and chives. Serve with extra cracked black pepper.
