Chop chocolate into ¼ callets or smaller. Set aside.
In a medium saucepan, combine cream and milk over medium-high heat, until it begins to simmer.
In a bowl, combine egg yolks, sugar, cocoa powder and salt. Whisk until fluffy and doubled in size (a couple minutes).
Remove saucepan from the heat and scoop out about 1 cup worth and add it into the egg mixture. Whisk until smooth.
Pour this egg and cream mixture back into the saucepan with the rest of the egg mixture and whisk.
Add saucepan back to the heat (medium), whisking constantly.
Fold in the chocolate gradually into the saucepan. Stir until melted.
Stir in vanilla.
When the custard coats the back of a spoon (about 2 minutes of stirring), turn off the heat.
Transfer custard to a preferred container to store in the refrigerator at least 5 hours (to overnight).
Pour cold custard into an ice cream maker and prepare to the maker's instructions.
Empty the canister into a freezer-safe storage container and place wax paper on the surface of the ice cream. Freeze until hard.
Serve with flake salt for garnish.