In A Large Saucepan, Saute Celery In 1 Tablespoon Butter Until Tender. Stir In The Soup, Mayonnaise, Sour Cream, Onion, Chicken, Water Chestnuts And Mushrooms. Cook And Stir Over Medium Heat Just Until Mixture Begins To Boil. Transfer To An Ungreased 13-In. X 9-In. X 2-In. Baking Dish. Sprinkle With Cheese. Unroll Crescent Roll Dough Into A Rectangle; Seal Seams And Perforations. Place Over Cheese. Melt The Remaining Butter; Toss With Nuts And Sprinkle Over Top. Bake, Uncovered, At 375 Degrees F For 20-25 Minutes Or Until Golden Brown.