Place the chocolate, butter, and vanilla extract in a large bowl and set aside.
1 cup semisweet chocolate chips, 2 tablespoons unsalted butter, 1 teaspoon pure vanilla extract
In a medium saucepan, whisk the sugar, cocoa, cornstarch, and salt together. Add the heavy cream, whisking until the mixture is smooth and lump-free. Whisk in the egg yolks until combined.
1 cup granulated sugar, ⅓ cup unsweetened cocoa powder, ¼ cup cornstarch, ¼ teaspoon kosher salt, 1 cup heavy cream, 3 large egg yolks
Place the saucepan over medium heat, then gradually whisk in the milk. Bring the mixture to a boil, whisking constantly as it thickens, then boil for 1 minute, until 200°F.
2 cups whole milk
Pour the mixture into the bowl with the chocolate, then whisk until melted and smooth.
Pour the mixture through a fine-mesh sieve into another bowl, pressing down on any lumps with a rubber spatula.
Place a piece of plastic wrap directly on the surface of the pudding, allowing it to cool slightly, then transfer it to the prebaked pie shell. Cover the pudding with the plastic wrap again, then chill the pie until set, at least 2-3 hours, up to overnight.
1 9-inch pie crust
Garnish with whipped cream and chocolate curls and serve.
2 cups whipped cream, Chocolate curls