Whisk together 1 cup cream and cocoa powder. Bring to a boil. Reduce heat and boil/simmer for 30 seconds whisking constantly.
Remove from heat and add chopped chocolate and whisk until smooth. Add remaining 1 cup of cream and whisk to combine.
Transfer mixture to a large bowl and position a fine mesh strainer over it. Set aside.
In a small bowl, whisk together egg yolks.
In a saucepan over medium heat, whisk together milk, sugar and sea salt.
Once the milk mixture is slightly warm, add ½ cup of warm milk to the beaten egg yolks and whisk to combine. Add the milk/egg mixture back into the saucepan, whisking during the addition.
Continue to cook the custard over medium heat, and stir the mixture constantly with a spatula until the it thickens and lightly coats the spatula (it does this when it reaches about 170 degrees F).
Pour the thickened custard through the metal strainer into the other ingredients in the bowl. Stir until combined. Discard any custard residue left on the strainer.
Add the vanilla and stir to combine.
Place a lid on top and let the mixture cool in the refrigerator for at least 6 hours, or overnight. To speed up the cooling process, you can place the container of the chocolate ice cream liquid base into an ice bath and stir it often.
Once the ice cream mixture is chilled, churn it in an ice cream maker until thick and frozen (30-40 minutes).
Transfer to an airtight container and freeze for at least 6 hours.
Serve!
