In a liquidiser or food processor, blend the vanilla biscuits and walnuts into fine crumbs. Transfer to a 23cm quiche dish. Mix in the butter and maple syrup. Using a fork, press firmly and evenly onto the bottom and sides of the dish to create a base. Chill 10 minutes in the freezer.
In a large bowl, blend the vanilla ice cream, pumpkin puree and spices. Spoon into the biscuit base. Smooth top with a spatula. Chill 1 hour in the freezer or until firm.
Before serving pie, place the double cream and caster sugar in a small bowl. Mix with an electric mixer on high speed until peaks form. Spoon into a piping bag with a star nozzle and pipe around the edge of the pie.
In a small saucepan over low heat, melt margarine and chocolate chips, stirring occasionally, until smooth. Transfer to a small plastic container and chill in the freezer 30 minutes or until firm.
Remove chocolate from container. Using a vegetable peeler or cheese slicer, scrape the chocolate to form small curls. Use the curls to decorate the pie