Pumpkin Chiffon Pie

For the Pumpkin Base - Adjust oven rack to lower-middle position and preheat to 400°F (205°C). Place squash halves cut-side down on a foil-lined aluminum baking sheet. Roast until fork-tender, about 45 minutes. When cool enough to handle, scrape pulp into a food processor and purée until smooth. Measure out 14 ounces (about 1 3/4 cups; 395g) squash purée (leftovers can be refrigerated for another use). Use warm, or refrigerate in an airtight container for up to 1 week.

For the Pumpkin Base - Add the water to a small bowl and sprinkle gelatin evenly on top. Let stand until gelatin absorbs the water and becomes translucent, about 5 minutes.

For the Pumpkin Base - In a 3-quart saucepan, add the egg yolks, sugar, milk, cinnamon, ginger, and nutmeg and whisk to combine. Turn the heat to medium and cook, whisking frequently, until mixture thickens slightly, about 5 minutes. A few bubbles are okay, but do not let it boil.

For the Pumpkin Base - Once the custard has thickened, reduce heat to low and stir in bloomed gelatin. Whisk until gelatin is completely dissolved and no lumps remain, about 45 seconds.

For the Pumpkin Base - Turn off heat and whisk in butternut squash purée and vanilla extract. Transfer mixture to a large bowl and chill in an ice-water bath, stirring occasionally, until cool to touch, about 10 minutes.

For the Swiss Meringue - Fill a wide pot with at least 1 1/2 inches of water, with a thick ring of crumpled tinfoil placed inside to act as a "booster seat." Place over high heat until steaming-hot, then adjust temperature to maintain a gentle simmer. Combine egg whites, sugar, cream of tartar, and salt in the bowl of a stand mixer. Set on foil booster seat over steaming water, stirring and scraping constantly with a flexible spatula, until egg whites hold steady at 175°F (79°C), between 8 and 10 minutes (if the temperature seems to be rising too slowly, crank up the heat). Transfer to a stand mixer fitted with a whisk attachment and whip at high speed until meringue is glossy and beginning to ball up inside the whisk, about 5 minutes.

For the Swiss Meringue - Divide Swiss meringue in half, reserving one half for another use or discard (see note). Add about one third of remaining meringue into cold squash mixture and fold gently with a flexible spatula just until incorporated. Fold in remaining meringue in two additions until combined.

To Assemble the Pie - Scrape filling into prepared, blind-baked crust and spread in an even layer. Cover loosely and refrigerate until filling is firm and cold, at least 5 hours and up to overnight.

To Assemble the Pie - When ready to serve, top pie with whipped cream and sprinkle with cinnamon. Slice into wedges with a hot chef's knife, rinsing the knife under hot running water between slices. Carefully slide a pie server under the crust, making sure it reaches all the way to the tip of each wedge, and serve.