wash .peel and chop celeriac into cubes. Simmer celeriac in all of the water with lid closed.
Add butter to soup pot.melt ,add the flour and cook until slightly bubbly,do not let brown or burn.Slowly stir in milk,simmer for 5 minutes stirring all the time.Add the boiling water from the celeriac.Puree the celeriac pieces in a blender add to the soup.
Season soup with lemon juice,salt,pepper and sugar.Chop the walnuts and whisk the cream.
Serve the soup in warmed soup bowls.Add a good spoonful of whipped cream and sprinkle with nuts.decorate with celeriac leaf if available
you can garnish with toasted bread of choice topped with the mushrooms ,
or you can mix two soups and serve as one,