Add flour butter and salt to a food processor. Pulse a couple of times until the mixture resembles breadcrumbs. Slowly add iced water until the dough comes together and forms a ball. Wrap it in clear plastic film and put in the fridge for at least 30-40 minutes. When ready to bake, heat oven to 350°F. Line 11x7 inch pan with parchment paper. Remove crust from fridge and roll it out into a 12x8" rectangle. With fingers, press crust into and on sides of pan. Cover crust with parchment paper, fill with baking beans and bake the crust for 7 minutes. Remove the beans and bake the crust for an additional 5 minutes. Cool completely before pouring the filling in. In large bowl, whisk the filling ingredients until smooth and well blended. Pour mixture into pan over cooled crust. Bake in the preheated oven for 50 minutes or until a knife inserted in centre comes out clean and centre is set. Remove from oven, place the pan on a cooling rack and cool completely. Refrigerate for 1 hour 30 minutes before cutting into bars. To serve, top each bar with whipped cream and a dusting of pumpkin pie spice. Store in fridge.