In a small bowl whisk together egg yolks and 3 tablespoons sugar, and set aside.

In a small saucepan, over medium heat whisk together, ½ cup sugar, cocoa powder, salt, and milk. As soon as the mixture starts to steam, slowly pour about ¼ cup of it into the egg yolks, whisking the yolk mixture vigorously the entire time. Return the chocolate mixture to the heat, and slowly add the yolk mixture, while continuing to whisk. This allows you to incorporate the eggs without causing them to scramble. Bring the entire mixture to a boil, whisking constantly. Remove from heat, and cool completely.

In a 4 cup measure or bowl, combine heavy cream, half and half, and vanilla. Whisk in the cooled chocolate custard, and stir until completely combined. Chill for 2 hours.