Melt butter in a large soup pot over medium heat.

Add sliced fresh mushrooms, chopped sweet onion, and chopped celery to the pot.

Cook the vegetables until they are tender, stirring occasionally.

Sprinkle all-purpose flour over the vegetables and stir well to coat.

Pour in chicken broth and simmer until the soup thickens.

Reduce the heat to low.

Stir in half-and-half, cooked wild rice, and chopped fresh marjoram.

Season with salt and pepper to taste.

Continue to cook over low heat until the soup is well heated and flavors have melded.