Start by chopping the chocolate and set it aside.
100 g semi-sweet chocolate, 75 g milk chocolate
Whisk the egg yolks, granulated sugar and vanilla paste until light and fluffy, takes about 2 minutes. Then add the cornstarch and cocoa powder and whisk until combined. Set it aside.
4 egg yolk, 50 g granulated sugar, 1 teaspoon vanilla paste, 40 g cornstarch, 20 g dutch process cocoa powder
In a medium sized saucepan add whole milk, espresso powder and granulated sugar. Place it on the stove over medium heat. Give it a stir until the granulated sugar has melted. Let it heat until it just starts steaming.
400 g whole milk, 50 g granulated sugar, 1 tablespoon instant espresso powder
As the egg/cocoa powder mixture is very thick, take the milk off the heat, and add a splash of the warm milk into the egg mixture and quickly whisk it to help loosen up the mixture. Then add about ⅓ more of the milk mixture, to temper the eggs. Be sure to whisk all the time so it doesn’t turn into scrambled eggs. Pour back the tempered mixture into the rest of the milk and place the saucepan back on the stove. Whisk constantly on low-medium heat until it has thicken.
Immediately pour the pastry cream into a clean bowl and add the chopped chocolate, butter and salt and with a whisk stir it together until melted and smooth. Pour the pastry cream into the crust and even it out.
30 g butter, ¼ teaspoon salt
Add some plastic wrap over the pie, so it touches the surface of the pie and set it to chill in the fridge for a minimum of 6 hours or preferably overnight.