Melt the butter in a soup pot over medium heat. Add the chopped mushrooms, celery, and leek. Cook until soften, stirring frequently.
Add flour and cook, stirring constantly, for 3 minutes.
Whisk in the broth gradually. Bring to a simmer and cook for 30 minutes.
Puree soup, then strain through a fine mesh strainer. Return soup to pot and place over low heat. Add the heated heavy cream and sherry, salt and pepper.
Serve in warm bowls.
Recipe by Farmhouse 1820 at https://farmhouse1820.com/cream-of-mushroom-soup/