Place flour, butter, sugar and salt into a large food processor. Pulse until coarse crumbs form.
While processor is running, add water 1 tablespoon at a time until a ball of dough forms. Shape into a disc and wrap in plastic wrap. Refrigerate for at least 30 minutes. (Tip: the dough can be made up to 2 days in advance.)
Heat oven to 375 F.
Combine all pie filling ingredients in a large bowl and beat with electric mixer until well combined.
Press crust dough into the bottom of a 9×13 baking dish that has been sprayed with cooking spray. (Note: I removed about ½ cup of the dough to roll out and make cutout leaves for decoration on top of the bars. I added them to the edge of the pan 30 minutes into the baking time, so they did not sink into the filling. You can skip this part and use all the dough for the crust; it will just be slightly thicker.)
Bake crust in preheated oven for 15 minutes.
Pour pie mixture over baked crust.
Bake another 50-60 minutes, until edges are set and filling is firm. Let cool completely and refrigerate until ready to serve.
Place heavy cream and maple syrup in a large bowl with electric mixer.
Beat on high until medium peaks form.
Dollop on top of pumpkin pie bar slices.
Sprinkle with cinnamon for garnish, if desired. Enjoy!