Preheat oven to 350℉
In a double boiler, melt the butter and unsweetened chocolate, over medium heat. Stir mixture until both chocolate and butter are combined. Remove from heat, and set aside.
In a medium mixing bowl, combine sugar, unsweetened cocoa, and coffee powder.
Add eggs one at a time, to the sugar, cocoa and coffee powder, until just incorporated.
Then add milk, vanilla and salt to the egg mixture.
Add the chocolate and butter mixture to the rest of ingredients, and whisk until well combined.
Pour the filling in the pie shell and bake.
Bake for 45-55 minutes