Sauté the leeks in a knob of butter in a large pot until soft.

Gently wash or brush the button mushrooms, quarter or halve them depending on their size, then add to the pot and brown them.

Add the chicken stock, a sprig of thyme and the soaked dried mushrooms. Stir thoroughly then let it simmer for 15 minutes.

Add the double cream and blend until smooth.

Mix the cornflour with a little water then add to the soup.

Cook for another 20 minutes to thicken. Serve with toast or croutons.