Dissolve the espresso powder. In a small bowl, dissolve instant 1 tsp espresso powder in 2 Tbsp pure vanilla extract with a whisk or fork.
Melt the chocolate. In a microwave safe bowl, combine 6 oz chocolate chips or chocolate shavings, 2 Tbsp butter, and 1 Tbsp water. Heat in a microwave in 30 second increments, stirring after each addition, until melted and smooth. Place in refrigerator to cool slightly.
Cook the eggs. Add 2 egg yolks, 2 tsp sugar, and the espresso-vanilla mixture to a sauce pan over medium-low heat. Whisk constantly until thickened, about 3 minutes, being careful not to overcook the eggs (or they'll scramble).
Stir in the eggs. Pour the cooked egg mixture into chocolate, then stir until very smooth. Return to the fridge.
Whip heavy cream. In the bowl of a stand mixer, whisk ¾ cup heavy cream until stiff peaks form. Carefully fold the heavy cream into the slightly cooled chocolate mixture until no streaks of cream remain.
Assemble the pie. Gently pour the chocolate mousse into the pie crust, smoothing out the top with a spatula. Place in a fridge to set, about 2-3 hours.
Top with whipped cream and serve. When ready, whip remaining ¾ cup heavy cream in the bowl of a stand mixer fitted with whisk attachment on medium-high speed. When soft peaks form, add 2 Tbsp confectioner's sugar. Continue whipping until stiff peaks form. Spoon the whipped cream on top of chocolate mousse pie, then sprinkle ¼ cup chocolate shavings on top. Serve immediately.