Make the Pie Crust: Process ¾ cup flour, sugar and salt in a food processor until combined, about two 1-second pulses. Add the butter and shortening and process until homogenous dough just starts to collect in uneven clumps, about 10 seconds; dough will resemble cottage cheese, but there should be no uncoated flour. Scrape the bowl with a rubber spatula and redistribute dough evenly around the blade. Add the remaining ½ cup flour and pulse until the mixture is evenly distributed around the bowl and the mass of dough has been broken up, 4 to 6 quick pulses. Turn the mixture into a medium bowl.
Sprinkle the vodka and ice water over the mixture. With a rubber spatula, use a folding motion to mix, pressing down on the dough until the dough is slightly tacky and sticks together. Flatten the dough into a 4-inch disk. Wrap in plastic wrap and refrigerate for at least 45 minutes or up to 2 days.
Remove the dough from the refrigerator and roll it out on a generously floured work surface to a 12-inch circle. Roll the dough loosely around the rolling pin and unroll into pie plate, leaving at least 1-inch overhang on each side. Ease the dough into the plate by gently lifting the edge of dough with one hand while pressing into plate bottom with other hand. Refrigerate for 15 minutes.
Trim the overhang to ½ inch beyond lip of pie plate. Fold overhang under itself; folded edge should be flush with edge of pie plate. Using thumb and forefinger, flute the edge of dough. Refrigerate the dough-lined plate for at least 2 hours.
Blind Bake Crust: Preheat oven to 350 degrees F. Line the chilled pie dough with aluminum foil and use granulated sugar to fill the whole pie plate. Bake for 40 minutes; remove the foil and sugar and set the crust aside while you make the filling.
Adjust oven rack to lowest position, place a rimmed baking sheet on the rack, and increase the oven temperature to 400 degrees F.
Prepare the Pie Filling: While the pie shell is baking, whisk cream, milk, eggs, yolks and vanilla together in a medium bowl. Combine the pumpkin, yams, sugar, maple syrup, ginger, cinnamon, nutmeg and salt in a large heavy-bottomed saucepan; bring to a sputtering simmer over medium heat, 5 to 7 minutes. Continue to simmer pumpkin mixture, stirring constantly and mashing yams against sides of pot, until thick and shiny, 10 to 15 minutes.
Remove the pan from heat and whisk in the cream mixture until fully incorporated. Strain the mixture through a fine-mesh strainer set over a medium bowl, using the back of a ladle or spatula to press solids through strainer. Rewhisk mixture and transfer to warm prebaked pie shell.
Bake the Pie: Bake pie on rimmed sheet for 10 minutes. Reduce oven temperature to 300 degrees F and continue baking until edges of pie are set and the center looks firm but jiggles slightly (an instant-read thermometer inserted in the center should register 175 degrees F), 20 to 35 minutes longer. Transfer pie to wire rack and cool to room temperature, 2 to 3 hours. Serve with whipped cream. Leftovers should be stored in the refrigerator for up to 3 days.
Pumpkin: Make sure you use pumpkin puree, not pumpkin pie filling (which includes extra sweeteners and spices).
Candied Yams: If you can't find candied yams, then canned yams or sweet potatoes in syrup will work, or you can use all pumpkin.
Make-Ahead Pie Crust: The pie dough can be prepared ahead of time and stored in the refrigerator for up to 5 days or in the freezer for up to 3 months.
Make-Ahead Baked Pie: You can bake the pie the day before you plan to serve it. Once the pie has cooled to room temperature, refrigerate overnight, then bring to room temperature before serving. Given the custard nature of this pie, it is not a good candidate for freezing; while you CAN do it, the filling will become a bit watery and the crust a bit soggy upon thawing.