1) Heat oil in a large saucepan over medium-high heat. Add leek and garlic. Cook, stirring, for 3 minutes or until leek has softened. Add potato. Cook, stirring, for 5 minutes.
2) Add stock. Season with pepper. Cover. Bring to the boil. Reduce heat to medium-low. Simmer for 15 to 20 minutes or until potato is tender. Set aside for 5 minutes to cool slightly.
3) Blend, in batches, until smooth. Serve.