Heat the oil in a pan. Sauté the shallot for approx. 5 mins. Add the radish (excl. leaves) and cucumber, cook briefly. Pour in the stock, bring to the boil, cover and simmer over a low heat for approx. 20 mins. Add the cream, blend until smooth.
Blanch the reserved radish leaves in boiling water for approx. 30 secs., dip briefly in ice-cold water, drain and chop finely. Mix in the cress and oil, season with salt. Divide the soup between bowls, finish with the oil, cream and radish.