Allenton Inn Cream of Mushroom Soup

6 tablespoons (3/4 stick) butter
1 pound sliced mushrooms
3 tablespoons flour
3 cups homemade duck stock (chicken stock may be substituted)
1 teaspoon salt
1/8 teaspoon freshly ground black pepper
1 teaspoon garlic powder
1 teaspoon packed brown sugar
1 cup whipping cream

Melt butter in large, heavy pan. Add mushrooms and cook over medium heat about 4 minutes. Remove mixture from heat and blend in flour. Return pan to heat and add stock slowly, stirring constantly. Add salt, pepper, garlic powder and brown sugar. Bring mixture to a boil, reduce heat and simmer about 5 minutes. Remove from heat and stir