Make the crust: In the bowl of a stand mixer fitted with the paddle attachment, pulse the flour, butter, and salt on medium speed until the butter has broken down into pea-size pieces. With the mixer on low speed, drizzle ¼ cup ice-cold water into the flour mixture, and mix just until the dough begins to form a ball, 45–60 seconds. Press the dough into a 1-inch-thick disk, wrap tightly in plastic wrap, and chill for at least 1 hour, or overnight.
Lightly flour a work surface. Retrieve and unwrap the dough. Using a rolling pin, and dusting the dough and the pin lightly with flour as needed, roll the dough into a 13-inch circle.
Transfer the dough to an 8-inch pie plate, then trim all but 1 inch of overhang from the edges. Crimp the edges as desired, then use a fork to poke small holes all over the bottom.
Freeze the pie plate until the dough is solid, at least 15 minutes, or up to 1 hour. Meanwhile, preheat the oven to 350°F.
Line the frozen shell with parchment paper or foil, and fill with pie weights or dried beans. Bake until lightly browned at the edges, 25–30 minutes. Carefully remove the weights and parchment, and continue baking until the bottom of the crust is cooked through, 5–6 minutes. Remove and set on a rack to cool completely.
Meanwhile, prepare the filling: In a small bowl, add ¼ cup cold water and sprinkle the gelatin on top. Set aside to let the gelatin “bloom.”
In a medium metal bowl, whisk the egg yolks, sugar, lemon juice, zest, and salt. Set the bowl over a medium pot filled 1-inch high with simmering water and cook, stirring occasionally, until the sugar is melted and the mixture has thickened slightly, 15–18 minutes. Remove from the heat, then whisk in the gelatin mixture until thoroughly combined. Let cool at room temperature, or refrigerate for 20–25 minutes, stirring frequently.
In the bowl of a stand mixer fitted with the whisk attachment, beat the egg whites on medium-high speed until stiff peaks form, 1–2 minutes. Using a rubber spatula, fold the whites into the cooled yolk mixture. Pour the chiffon into the baked pie shell, smoothing the surface with the spatula. Refrigerate for at least 4 hours, or overnight.
To serve, in the bowl of a stand mixer fitted with the whisk attachment, whip the cream and vanilla on medium-high speed until medium peaks form, 2–3 minutes. Use a spatula to spread the cream over the surface of the pie, or pipe the cream in dollops around the center or edges.