1.Heat butter in a large saucepan over medium heat. Add leek, garlic and potato, cook, stirring, 3 minutes or until leek softens.
2.Add stock and cream, bring to the boil, reduce heat, simmer, covered, for 5 minutes or until potato is tender. Add peas and mint, simmer, 10 minutes. Season to taste, cool 10 minutes.
3.Blend or process soup mixture until smooth, thinning with a little water if soup is too thick. Pour among -cup heatproof glasses, cups or shot glasses. To serve, drop teaspoons of sour cream onto soup, sprinkle with pepper.