Combine the flour, sugar, and salt in the bowl of a large food processor and pulse a few times to combine.
Add the cold cubed butter and shortening, and pulse in short bursts until they're cut into the dry ingredients and the mixture has the texture of coarse crumbs. Add half of the cold water and pulse in 5-second bursts, adding the rest a little more at a time just until the dough starts to come together. You may not need to use all of the water—stop when the dough starts to come together, and don’t overwork it!
Turn the dough out onto a lightly floured board and knead it just enough to incorporate any dry patches of flour. Wrap the dough well in plastic wrap, and refrigerate it for an hour to chill. The dough can be made several days in advance and kept in the refrigerator until ready to use.
Flour your work surface and rolling pin. Roll the dough out into a circle, and press it into a 9-inch pie pan. Crimp the edges of the pie, and place in the freezer while you preheat the oven to 400 F.
Once at 400 F, spray a piece of foil with nonstick cooking spray and press it on top of the pie. Fill it with pie weights, rice, or beans, and bake for 20-25 minutes, until the dough no longer looks raw and is starting to cook along the edges. Remove the foil and weights, and if the crust puffs up on the bottom, gently press it down again. Cool the par-baked crust to room temperature before using it.
To Make the Pumpkin Pie:
Preheat the oven to 350 F. Whisk together the pumpkin and dulce de leche until smooth and free of lumps. Add the remaining ingredients and whisk until smooth. Pour into the par-baked crust and smooth into an even layer.
Bake the pie at 350 F for 50 minutes, or until it barely jiggles when you tap it. If the edges of the crust seem to be getting too dark, cover the edges with a ring of aluminum foil. The pie can be served warm or cool, and can be kept for several days in the refrigerator.
To speed things up, you can use a pre-made pie shell, or purchased pie dough, instead of making your own. If you cannot find dulce de leche, see the Note at the bottom about making your own from condensed milk. Note: If you cannot find prepared dulce de leche, you can make your own on the stovetop, using a can of sweetened condensed milk. Place the can of condensed milk in a deep saucepan, and fill the pan with water so that the can is completely submerged. Bring the water to a simmer and allow it to simmer for 4 hours. Several times an hour, check the saucepan to make sure that the water is still covering the top of the can, and add water as necessary. After 4 hours, remove the can and let it cool completely before using it. You can also just use condensed milk in this recipe, to make a "normal" pumpkin pie instead of a dulce de leche version.