If your ice cream maker requires pre-freezing the bowl, do so for the recommended period. Or follow the instructions of whatever machine you have.
separate your cream. Put, one cup in a pot. Keep the rest cold. Add the cocoa, vanilla, sugar, and salt to the cream in the pot, and bring to a boil stirring occasionally. Remove from the heat.
In a separate Mixing bowl, whisk the egg yolks. Slowly add the hot cream mixture a little at a time, whisking continuously. Return the mixture to the pot, add the chocolate, and bring to a simmer. Do not boil or it will curdle the egg. You want a gentle heat, whisk the whole time, until the mixture thickens. Make sure nothing sticks to the bottom of the pan.
When thickened, transfer the mix to a stainless steel bowl, and cool. Whisk in the rest of the cream until well blended. Then transfer to the ice cream maker.
Follow instructions for ice cream machine to finish. My machine requires 20 minutes of churning, followed by an hour or 2 holding the ice cream in the freezer.
Enjoy with your favorite toppings or by itself.
