Line a 9-inch square baking dish with two 24-inch sheets of plastic wrap, allowing excess to hang over sides. Arrange 9 cookies in pan and 3 cookies standing up along each side.
Warm peanut butter in microwave for 30 seconds; drizzle 1/4 cup on cookies in pan. Spoon chocolate-chip ice cream on top and cover with 8 cookies. Repeat layering twice with 1/4 cup peanut butter, a pint of ice cream and more cookies. Cover with overhanging plastic wrap and press down to compress layers. Cover with second sheet of plastic and freeze for at least 3 hours and up to 1 week.
To unmold, dip pan into warm water, unwrap cake and invert a platter on top. Flip cake over and remove pan and wrap. Return cake to freezer.
Whip cream and confectioners' sugar until stiff. Spread on cake and sprinkle with chocolate, if desired.