Make the Shortbread Crust: Preheat oven to 425 degrees F. Combine butter, sugar, salt, and flour with your mixer until it resembles coarse sand. Add the water slowly with the mixer, until the dough forms. Line a 9 x 13-inch baking dish with parchment paper. Let some of the parchment paper hang over the edges. Press the dough into the baking dish in an even layer, using your fingers. Bake the shortbread crust for about 15 minutes, or until it becomes light golden brown on top and it set in the middle. Remove from oven, set aside.

Make the Pumpkin Filling: Reduce oven to 350 degrees F. Whisk all of the filling ingredients in a large bowl until combined. Pour the pumpkin filling over the crust and bake for 40-45 minutes or until the center is set and no longer jiggly. Remove from oven and let it cool for about an hour. If you prefer your pumpkin pie chilled, place it in the fridge for at least another hour

To Serve: Pull the bars out of the baking dish by holding the parchment paper. Cut into squares. Top with whip cream and a sprinkle of cinnamon.