1.In a large saucepan, heat the oil and add leek and garlic. Cook, stirring, until leek is soft but not coloured.
2.Add the stock, water, lettuce and peas; bring to the boil. Reduce the heat; simmer 15 minutes or until the peas are soft. Remove from heat; add the sugar and mint. Stand 5 minutes.
3.With a hand blender or food processor, blend or process soup until smooth. Return soup to saucepan; stir over heat until hot. Season to taste with sea salt and freshly ground black pepper.