Place the chopped chocolate in a large heatproof bowl. Warm 1 cup of the cream with cocoa powder in medium saucepan, whisking to thoroughly blend the cocoa. Bring to boil then reduce heat and gently simmer for 30 seconds, whisking constantly.
Remove from heat and pour the mixture over the chopped chocolate, scraping the saucepan clean as much as possible. Let stand for about 1 minute. Stir the ganache until smooth. Add in the remaining cup of cream and mix well. Place a mesh strainer atop the bowl and set aside.
Warm the milk, sugar and salt in the same saucepan. In a separate medium bowl, whisk together the egg yolks. Slowly pour the warm milk into the egg yolks, whisking lightly but constantly, then scrape the warmed yolks back into the saucepan. Switch to a wooden spoon and stir the mixture constantly over medium heat, making sure to scrape the bottom and corners of the pan. Stir until the mixture thickens and reaches nappe consistency (the custard should coat the back of the spoon).
Pour custard through the strainer into the chocolate mixture and stir until smooth, then add in the vanilla. Continue to stir over an ice bath until cool. Refrigerate the mixture to cool thoroughly (I let it cool overnight). Freeze the custard in your ice cream machine following the manufacturer’s instructions.