In a medium saucepan, combine 1 cup of the cream with cocoa powder over medium-high heat. Whisk to dissolve cocoa and bring the mixture to a boil.
Reduce heat to medium-low and simmer for about 1 minute, whisking constantly. Remove from heat and add the chopped semi-sweet chocolate, stirring until smooth.
Stir in the remaining 1 cup cream. Transfer mixture to a mixing bowl and set a large fine mesh strainer over the top. Set aside.
Using the same saucepan combine milk, sugar, and salt over medium-high heat.
In a separate bowl whisk together the egg yolks. When the milk mixture is warm slowly pour it into the egg yolks, whisking constantly. (Not too fast or you’ll scramble the eggs). Then, pour the egg-milk mixture back into the saucepan.
Stir the mixture continually over medium heat, scraping the bottom as you go to avoid a bottom film, until it thickens into a custard and coats the spoon/spatula. If you have an instant-read thermometer, it should read 170-175°F.
Pour custard through the strainer into the chocolate mixture that you had set aside. Add vanilla extract and stir until smooth and creamy.
Cover with plastic wrap and refrigerate overnight.
Using a 1 ½ quart ice cream maker, churn using manufacturer’s instructions.
Freeze at least 4 hours or until desired firmness. Store in an airtight container in the freezer.