To make the crust, whisk the flour and salt in a large bowl. Add the cold butter cubes. Use a pastry blender or your fingertips to cut the butter into the flour until the mixture resembles coarse crumbs with some pea-sized pieces remaining. Gradually stir in 1 cup of ice water until the dough just comes together. Do not overmix. Divide the dough into two pieces: one about three-fourths of the dough, and the other the remaining one-fourth. Form each into a flat disk, wrap in plastic, and refrigerate for at least 30 minutes.
Preheat your oven to 425°F (220°C). Line a small baking sheet with parchment paper. On a floured surface, roll out the smaller disk of dough to 1/8-inch thickness. Use small cookie cutters to cut out decorative shapes, like leaves or pumpkins. Place about half of the cutouts on the prepared baking sheet and refrigerate the other half. Sprinkle the cutouts on the baking sheet with sanding sugar, if using. Bake for 5-7 minutes, until light golden. Let them cool completely; these are for garnish later.
For the filling, lightly beat the eggs in a large bowl. Add the brown sugar, heavy cream, pumpkin puree, pumpkin pie spice, and salt. Whisk until everything is smooth and well combined, but be careful not to overmix.
On a lightly floured surface, roll the larger disk of dough into a 19x14-inch rectangle. Carefully transfer the dough to an ungreased 15x10x1-inch jelly roll pan. Press it into the bottom and up the sides. Trim any excess and crimp the edges as you like.
Pour the pumpkin filling into the crust and spread it evenly. Arrange the unbaked, refrigerated dough cutouts on top of the filling.
Bake for 10 minutes at 425°F (220°C). Then, reduce the oven temperature to 350°F (175°C) and continue to bake for 50-60 minutes. The pie is done when a knife inserted near the center comes out clean and the filling is set. The internal temperature should be at least 175°F (79°C).
Let the pie cool completely on a wire rack for at least 2 hours. The filling will continue to set as it cools.
Just before serving, make the whipped cream. In a chilled bowl with an electric mixer, beat the cold heavy cream, caramel sauce, and powdered sugar on medium-high speed until stiff peaks form.
Cut the cooled pie into squares. Serve each slice with a dollop of caramel whipped cream and one of the baked pastry cutouts for garnish.