Kervelsoep (chervil soup)

Instructions

1. Peel the potatoes and the onion, then cut them into small dice.
2. Melt the butter in a saucepan, add the onion and sweat it for 3 minutes without colouring.
3. Sprinkle in the flour, stir for 1 minute, then gradually pour in the hot stock while whisking.
4. Add the potatoes and cook for 15 minutes over low heat, until tender.
5. Meanwhile, rinse the chervil, remove the stems and finely chop the leaves.
6. Blend the soup until smooth, then return it to low heat and stir in the chopped chervil.
7. Mix the cream with the egg yolk, pour it into the soup off the heat while stirring, season and serve straight away.