Melt butter in a heavy-bottomed pan.

Add the onions and sweat.

Add celery root and chestnuts and cook for 5–6 minutes.

Season with a pinch of salt.

Add stock and bring to boil.

Reduce the heat and simmer until celery root is tender and very soft.

Purée the soup using a hand blender or carefully in a pitcher blender.

Return to the heat and add cream.

Bring to a simmer and cook to desired consistency.

Prior to serving, adjust the seasoning with salt and grate in whole nutmeg, about ¼ teaspoon. Serve garnished with chopped chestnuts and celery leaves.