How to Make It
Combine milk, cocoa powder, and instant coffee in a saucepan. In a separate bowl, whisk together sugar, cornstarch, and salt. Add egg yolks to sugar mixture and whisk until lightened in color, 1 to 2 minutes.
Place saucepan with milk over medium-high and heat while whisking until just beginning to steam but not boiling. Remove from heat. Slowly stream 1 cup of the warm milk mixture into the egg yolk mixture while whisking. When completely combined, return saucepan to medium heat, and whisk milk while slowly streaming in the egg mixture. Whisk constantly until mixture thickens and a few bubbles break the surface while whisking, about 5 minutes. Remove from heat and stir in butter, vanilla, and 2 ounces chopped chocolate until fully melted and combined.
Pour pudding filling into graham cracker crust and spread evenly with a spoon. Refrigerate for at least 3 hours. Garnish with whipped cream and chopped chocolate.