Set the oven to 350°F (175°C) to ensure it is fully heated before baking.
Prepare the filling.
In a medium mixing bowl, combine the sugar, melted butter, cocoa powder, eggs, vanilla extract, and evaporated milk. Using an electric mixer, beat the mixture on medium speed for 1–2 minutes until smooth and well blended.
Fill the crust.
Pour the prepared chocolate mixture into the unbaked pie crust, smoothing the top evenly.
Bake.
Place the pie on the center rack of the oven and bake for 40–45 minutes. The center should appear slightly jiggly when removed, as it will continue to set while cooling.
Cool.
Transfer the pie to a wire rack and allow it to cool for at least 1 hour before serving. For a firmer texture, refrigerate the pie until fully set.
Notes
To make this Chocolate Chess Pie gluten-free, use a certified gluten-free pie crust in place of a standard crust. Confirm that the cocoa powder and vanilla extract are also certified gluten-free to avoid cross-contamination.