Make the crust: Pulse the flour, granulated sugar and salt in a food processor to combine. Add the shortening and pulse until the mixture looks like cornmeal. Add the butter and pulse until it is in pea-size pieces. Add the vinegar and 2 tablespoons ice water; pulse until the dough just comes together but is still crumbly. Turn out onto a piece of plastic wrap; shape into a disk and wrap. Refrigerate until firm, at least 1 hour or overnight.
Roll out the dough into a 12-inch round on a lightly floured surface. Ease into a 9 1/2 -inch deep-dish pie plate. Fold the overhanging dough under itself and crimp with your fingers or a fork. Refrigerate until firm, about 30 minutes.
Preheat the oven to 350 degrees F. Line the crust with foil, then fill with pie weights or dried beans. Bake until lightly golden around the edge, about 20 minutes. Remove the foil and weights and continue baking until golden all over, about 15 more minutes. Transfer to a rack and let cool completely.
Meanwhile, make the filling: Spread the walnuts on a baking sheet; bake until toasted, about 7 minutes. Let cool completely.
Dissolve the gelatin in 1/4 cup warm water. Whisk the maple syrup, granulated sugar, 1/4 cup heavy cream and the eggs in a saucepan over medium heat. Cook, stirring constantly with a wooden spoon, until slightly thickened, about 7 minutes. Let cool slightly, then stir in the dissolved gelatin and maple extract until smooth. Cover and refrigerate until just cooled and pudding-like, about 15 minutes.
Beat the remaining 1 3/4 cups heavy cream and the confectioners' sugar in a large bowl with a mixer on medium-high speed until soft peaks form, about 3 minutes. Transfer 2 cups of the whipped cream to a medium bowl and fold in 1/2 cup toasted walnuts, then fold the walnut whipped cream into the chilled maple pudding until well combined. (Set aside the remaining walnuts and refrigerate the remaining whipped cream for topping.)
Pour the filling into the cooled crust. Refrigerate until firm, 2 to 4 hours. Top with the remaining whipped cream and walnuts just before serving.