Combine all the crust ingredients and mix until well combined and it resembles wet sand and clumps together in between your hands.
Place the crumb mixture into a well-greased pie dish. Use the back of a measuring cup to flatten the bottom of the crust into the bottom and sides of the pan. Use both hands to crimp up the sides. Bake at 350°F for about 10 minutes. Then, allow the crust to cool for 10 minutes out of the oven.
Meanwhile, work on the filling. Combine the egg yolks, brown sugar, granulated sugar, cinnamon, nutmeg, pumpkin pie spice, salt, vanilla, maple syrup, and sour cream in a large bowl and whisk until well combined. Add in the pumpkin puree and whisk until combined and the mixture is smooth. Set aside.
In the bowl of your stand mixer, pour in your cold heavy cream, and using your whip attachment, whip on high speed until soft peaks are achieved.
Carefully add the whipped cream to your pumpkin mixture all at once and carefully fold in until just combined.
Wipe the residual cream from the bowl with a paper towel and wash off the whip attachment and dry. Add in your egg whites and sugar all at once. Beginning at medium speed and then progressing to high speed, whip until medium peaks are achieved. The egg whites should be glossy and white.
Add in the whipped egg whites into the pumpkin mixture and carefully fold in until uniform in color and everything is combined.
Carefully pour the filling into your prepared crust. Use an offset or rubber spatula to gently smooth the top as smooth as possible. Bake in a preheated oven at 325°F for about 40-50 minutes or until the outsides are set but the inner portion is still slightly jiggly, but not liquid to the touch. It's very similar to cheesecake or creme brule since this is also a custard.
Allow the pie to cool at room temp for an hour then gently cover with aluminum foil making sure the foil doesn't touch the top of the pie. Cool in the fridge overnight. Decorate as you please and enjoy!
Where does the cornstarch go in? It's not mentioned in your instructions. Thanks!