PreparationFilling: 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. Let pudding cool 5 minutes, whisking every minute. 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.
PreparationFilling: 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. Let pudding cool 5 minutes, whisking every minute. 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.