Whisk sugar, cocoa, flour, and espresso powder (if using) and salt together. Pour butter and evaporated milk into sugar and cocoa mixture and beat on high speed. Add vanilla and eggs. With mixer speed on high speed, mix for approximately 2-3 minutes to lighten.
Pour mixture into 9 inch unbaked pie shell and bake for about 55 minutes. The center of the pie will be a bit soft. Allow to cool on a wire rack for at least an hour before slicing. The pie will continue to set as it cools.
Notes
Storage, Make Ahead, and Freezer InstructionsTo store leftovers. Cover the pie loosely with wrap and store it in the refrigerator for up to 3 days.To make ahead. This pie is excellent to make ahead as it is best served cold! Like with the storage instructions, make the pie ahead of time and cool. Cover the pie loosely with wrap and store in the refrigerator for up to 3 days. Remove from the refrigerator, slice, and serve.To freeze. You can easily freeze a baked Chocolate Chess Pie. Bake and cool completely. Wrap tightly with freezer-safe wrap and place in a freezer bag. Freeze for up to 3 months. To serve, thaw in the refrigerator overnight and then slice and serve.