INGREDIENTS:
Crust
2 Tbsp. granulated sugar
2 tsp. Diamond Crystal or 1 tsp. Morton kosher salt
2⅔ cups all-purpose flour, plus more for dusting
1½ cups (3 sticks) chilled unsalted butter, cut into ½" pieces
Filling
½ cup sugar
3 Tbsp. unsweetened cocoa powder, preferably Dutch-process
2 Tbsp. cornstarch
2 large eggs
2 large egg yolks
2½ cups whole milk
1 tsp. vanilla extract
½ tsp. kosher salt
4 oz. bittersweet chocolate, chopped
Assembly
1 tsp. unflavored powdered gelatin
2 cups heavy cream
2 Tbsp. sugar
2 tsp. vanilla extract
1 tsp. kosher salt
Unsweetened cocoa powder, preferably Dutch-process (for serving; optional)
INSTRUCTIONS:
Crust
Whisk sugar, salt, and 2⅔ cups flour in a large bowl. Add butter and, using your fingers, smash each piece into a thin disk. Take your time doing this and don’t feel compelled to break butter into even smaller pieces. Drizzle ⅔ cup ice water over, dispersing it as widely as possible, and mix with a rubber spatula to bring mixture together into a shaggy mass.
Turn dough out onto a surface and work together with your hands, pushing and flattening until dough holds together when squeezed in your palm but some streaks of dry flour are still visible. Divide dough into 2 portions.
Flatten 1 portion of dough into an 8"-diameter disk. Cut into quarters, stack pieces on top of one another, and flatten dough with a rolling pin to about half of its original height. At this point dough should hold together with no dry spots remaining, and have nice big flakes of butter showing. Use a bench scraper or a large knife to clean any clingy bits of dough from surface. Dust surface with flour, then dust top of dough with flour. Roll out to a ¼"–⅜"-thick round. Wrap dough around rolling pin and transfer to a standard 9"-diameter pie dish. Unfurl into dish, then lift edges and allow dough to slump down into dish. Trim overhang to an even 1" (there will be some excess). Fold overhang under and crimp as desired. Cover and chill until very cold, at least 1 hour and up to 12 hours (cover tightly if chilling longer than 1 hour). Repeat process with remaining dough and another pie dish. Or form into a 1½"-thick disk, wrap in plastic, and chill up to 3 days (or freeze up to 1 month).
Place a rack in middle of oven; preheat oven to 400°. Lay 2 sheets of parchment paper over dough and fill with pie weights or dried beans (they should fill the dish). Set on a foil-lined rimmed baking sheet (this will keep any butter drips from smoking up your oven). Bake until edges are golden brown and bottom is opaque (carefully lift parchment to check), 30–35 minutes. Remove from oven; reduce oven temperature to 300°. Lift out parchment and weights. Bake crust until evenly chestnut brown all over, 10–15 minutes. If baking both crusts, turn oven dial back up to 400° and let oven preheat; repeat with remaining crust.
Filling
Whisk sugar, cocoa powder, and cornstarch in a large saucepan to combine. Add eggs and egg yolks and whisk vigorously, making sure to get into corners of pan, until smooth. Whisk in milk, vanilla, and salt.
Place saucepan over medium heat and bring to a simmer, whisking often and making sure to get into corners of pan, 8–10 minutes (mixture should be bubbling and thickened). Reduce heat and continue to simmer, whisking constantly, 3 minutes. Remove from heat and let pudding cool 5 minutes, whisking several revolutions every minute to prevent any skin from forming.
Add chocolate to pudding and whisk until melted and fully incorporated. Scrape filling into pie crust; smooth surface. Chill until cold and set, at least 2 hours and up to 3 days.
Assembly
Stir gelatin and 1 Tbsp. water in a small bowl. Let sit until solidified, about 5 minutes. Microwave in 5-second intervals until melted, or set in a bowl of very hot water and let sit until melted.
Using an electric mixer, beat cream, sugar, vanilla, and salt in a large bowl until soft peaks form. Add melted gelatin and beat until medium peaks form. Spoon whipped cream over filling, swirling as desired. Chill until set, about 1 hour. Dust with cocoa powder if desired.
Do Ahead: Pie can be made 3 days ahead. Keep chilled.