To make the pesto, place parsley, cheese, pine nuts and oil in the bowl of a small food processor and process to combine. Set aside.
Melt butter in a large saucepan over high heat. Add the onion and garlic and cook for 2–3 minutes or until softened. Add the potato and stock and cook for 15–20 minutes or until potatoes are tender. Add milk and cook for 1–2 minutes or until warmed through. Remove from heat, add cheese and blend with a stick mixer until smooth. Top with the pesto to serve. Serves 4.