Leftover Meat Pie
["mashed potatoes (instant works well, for 4 people)", "1 large onion, cut in 1-inch pieces", "1/4 c. butter or margarine", "1/4 c. flour", "1 1/2 c. warm milk", "2 bouillon cubes", "1/2 tsp. salt", "1/4 tsp. pepper", "1/4 tsp. celery salt", "2 c. cooked meat, cut into 1-inch pieces", "1 can peas and carrots", "1 can mushrooms"]
["Brown onion in butter.", "Add flour, stock and seasonings.", "Cook until thick, then simmer about 5 minutes.", "Add meat and vegetables."]
["potatoes", "onion", "butter", "flour", "warm milk", "bouillon cubes", "salt", "pepper", "celery salt", "cooked meat", "peas", "mushrooms"]