Shrimp and cucumber soup

1. Peel cucumber skins off thinly, using a potato peeler. Halve the cucumbers lengthways, using a sharp knife, then remove the seeds with a teaspoon and discard. Slice scooped-out cucumber into crescents and set one quarter aside for garnish.
2. Melt the butter in a saucepan and add remaining cucumber. Cook over low heat for 10 minutes. Mix cornflour with a little water. Stir into cucumbers and gradually add chicken stock, stirring constantly.
3. Heat the milk with the onion. Strain and add resulting milky liquid to cucumber mixture. Bring to boil and simmer for 10 minutes, cool slightly and either purée in a blender or rub through a fine-mesh sieve. If the soup is too thin, add extra cornflour mixed to a paste with water and cook, uncovered, over fairly high heat until it thickens (becomes more concentrated, or reduced).
4. Just before serving, blend cream and seasoning in lightly. Pour into chilled soup bowls and fold in reserved cucumber and most of shrimps. Sprinkle with dill and reserved shrimps. Serve the soup lightly chilled, not ice cold (because the particles of butter will congeal).