In a medium saucepan add 1 cup of the cream and the cocoa powder, whisk until the cocoa powder is combined. Bring the mixture to a boil, and reduce heat and simmer at a very low boil for 30 seconds, whisking constantly.
Remove from the heat and add in the chopped chocolate, let it stand for 3 minutes and then stir until smooth.
Stir in the remaining 1 cup of cream.
Pour the mixture into a large bowl, scraping the saucepan as thoroughly as possible, and set a mesh strainer on top of the bowl
MAKE THE CUSTARD:
Add the milk, sugar, and salt to the same saucepan and heat over medium heat until warm.
Whisk the egg yolks together in a medium bowl. Slowly whisk in 1/2 cup of the warm milk into the egg yolks, and then whisk the yolk mixture into the saucepan with the remaining milk.
Whisk the milk and egg yolk mixture CONSTANTLY over medium heat while scraping the bottom and edges of the saucepan as you stir. Keep stirring until the mixture reaches 170°F on an instant-read thermometer and it has thickened and coats the back of a spatula.
COMBINE THE CHOCOLATE AND CUSTARD MIXTURES:
Pour the custard through the strainer into the chocolate mixture and whisk until smooth, then stir in the vanilla.
Cover and chill the mixture in the refrigerator for at least 3 hours, or overnight.
FREEZE THE ICE CREAM:
Next, freeze it in your ice cream maker according to the manufacturer’s instructions.
Place the ice cream in containers and freeze for at least 2 hours before scooping and serving.
This recipe makes a little more than 1 quart (4 cups) of ice cream.