Bake your pie shell according to package directions or your favorite homemade recipe. Let it cool completely before filling.
Make the Chocolate Filling:
In a medium saucepan, whisk together sugar, cocoa powder, cornstarch, and salt. Gradually whisk in milk until smooth. Cook over medium heat, stirring constantly, until the mixture thickens and begins to bubble — about 8–10 minutes.
Temper the Eggs:
In a small bowl, whisk the egg yolks. Slowly add a small amount of the hot chocolate mixture to the yolks while whisking to prevent curdling. Then pour the yolk mixture back into the saucepan and continue cooking for 2–3 more minutes, stirring constantly, until thick and glossy.
Add Butter and Vanilla:
Remove from heat and stir in butter and vanilla until smooth.
Fill the Pie Shell:
Pour the warm chocolate filling into the cooled pie crust. Smooth the top with a spatula.
Add Topping (Optional):
For meringue, spread it over the hot filling and bake at 350°F (175°C) for 10–12 minutes, until golden.
For whipped cream, let the pie cool completely before topping.
Chill and Serve:
Refrigerate the pie for at least 3 hours before serving to allow it to set. Slice and enjoy chilled.
