Beef Wellington
["2 to 2 1/2-pound beef tenderloin (filet mignon)", "1/2 package (17 1/4-ounce size) Pepperidge Farm", "Frozen Puff Pastry Sheets (1 sheet)", "1 egg", "1 tablespoon water", "1 tablespoon margarine or butter", "2 cups finely chopped mushrooms (6 ounces)", "1 medium onion, finely chopped (about 1/2 cup)"]
["Preheat oven to 425\u00b0", "Place meat in lightly greased roasting pan. Sprinkle with pepper if desired. Roast at 425\u00b0", "for 30 minutes or until thermometer reads 130\u00b0.", "Cover and refrigerate 1 hour."]
["tenderloin", "Pastry", "egg", "water", "margarine", "mushrooms", "onion"]