Peel and finely dice the shallot. Separate the watercress leaves from the stalks and place in two bowls. Peel and chop the garlic. Peel and dice the potatoes.
Heat a saucepan and melt the butter. Add the shallot and sweat with a pinch of salt. Once transparent, add the garlic, the potatoes and the watercress stalks. Deglaze with the white wine and reduce to a third. Add the vegetable stock, bring to the boil and cook until the potatoes are soft. Blitz in a food processor until smooth and then add the watercress leaves and continue blitzing until bright green. Pass through a sieve and check the seasoning.
Chop the chives and mix with the creme fraiche.
Serve the soup with a dollop of creme fraiche.
«Add the watercress leaves at the very end to ensure your soup is a bright green colour.»