Bring a large pot of salted water to a boil. Add potatoes and cook until tender, about 15 minutes. Drain.
Meanwhile, melt 1 tablespoon butter in a small saucepan over medium heat. Saute celery and onion for about 8 minutes, or until tender.
To the cooked potatoes add the celery and onion, 2 tablespoons butter, 1/4 cup cream, celery salt and ground black pepper. With an electric mixer on low, beat until desired consistency is reached.
To make the gravy melt 2 teaspoons butter in a small saucepan. Add flour and cook 5 minutes, stirring constantly. Gradually whisk in chicken broth and cook over medium-high heat until thickened. Stir in 1/3 cup cream and onion powder; heat through.
