Wearing gloves, pick the top four leaves of the nettles, avoiding any old or tough leaves.
Wash the nettles thoroughly.
In a large pot, sweat the chopped onions, leeks, celery, and garlic in butter until soft, about 10 minutes.
Add the stock and bring to a simmer.
Add the washed nettles to the simmering stock, stirring as they wilt. Simmer for 5 minutes until the stems are tender.
Add salt and pepper to taste.
Blend the soup until smooth.
Serve with a dollop of crème fraîche, chopped chives, and freshly ground black pepper.