Combine cocoa, 1 1/2 cups of the sugar, cornstarch and salt in a saucepan. Gradually stir in the milk. Cook and stir over medium heat until mixture comes to a boil and stir for 1 minute more. Remove from heat.
Quickly beat eggs with the 1/2 cup remaining sugar until well blended. Blend a small amount of the hot mixture into the beaten eggs to temper and add egg mixture to the saucepan. Continue cooking stirring all while until temperature reaches 170 degrees F. on a candy or instant read thermometer. Remove from heat. Blend in vanilla and both creams.
Remove to a container and chill.
Freeze in ice cream freezer according to manufacturer''s directions.