Prepare a pie shell in an 8 or 9 inch pan.  Blind bake the shell to completely done.  Allow to cool at room temperature while the filling is made.

In a bowl over a pot of simmering water, melt the butter and chocolate together to just melted.  Remove from heat and let stand at room temperature.

Whip the egg whites in the mixing bowl at slow speed, to start. Turn the speed to medium and sprinkle in the 1/4 C of sugar. Turn the mixer to full speed and whip the whites to medium-stiff peaks.  Transfer the whites to a clean bowl for later use.

Whisk the egg yolks and 1/2 C of sugar in the same bowl of a stand mixer. Beat them until very thick and pale yellow.  Add the coffee, the vanilla, and the cooled chocolate/butter mixture.  Stir with whisk attachment to incorporate and scrape the bottom of the bowl with a rubber scraper.

Re-whip the whites to bring them to stiff peaks. Add a small portion of the whites to the chocolate mixture, then fold the remaining whites into the base 4 additions.

It is a matter of personal preference if the whites are streaky. I don't mind a few streaks in my chocolate mixture

Pour the filling into the prepared pie shell.  Cover the filling with plastic wrap and cool for at least 4 hours.

Whip the heavy cream on medium speed or by hand slowly until the cream develops some volume.  Add the sugar and finish whipping until it reaches stiff peaks. 

Top the pie.  Keep the whipped cream mounded in the center and spread over the pie to the edge.  It can be topped just when finished or just before service.

Garnish with shaved chocolate or chocolate jimmies.