In a medium bowl add the egg yolks and half the sugar. Mix to combine and set aside.
In a medium pot add the cocoa powder, the rest of the sugar and ¼ cup of milk. Mix to create a paste. (See note) Then add the rest of the milk, heavy cream and salt. On medium heat bring mixture to a simmer.
Add a ¼ cup of the hot mixture to the bowl with the yolks. (See notes) Once you have added about ½ cup of the hot mixture, pour the egg mixture back into the pot.
Cook the mixture on medium low heat for another 5 minutes or until mixture has thickened. You will know it’s ready when you can coat the back of a spoon and when you run your finger down the spoon and the mixture stays separated.
Pour the mixture through a mesh strainer into a clean bowl. Put the bowl into a larger bowl to create an ice bath. This will help cool the mixture down before putting it into the fridge. Once cooled, put plastic wrap on top and refrigerate at least 2 hrs or overnight.
Freeze in your ice cream machine according to the manufacturer's instructions.