In a medium saucepan, combine sugar, cocoa powder, arrowroot starch and salt.
Slowly whisk in the milk, mixing to combine
Place the saucepan on medium heat and whisk until it starts bubbling, add chocolate chips
Place egg yolks in a bowl and whisk until frothy, slowly pour a half a cup of the warm chocolate mixture until fully combined
Pour the egg yolks into the pot and whisk until thickened, about 3 minutes.
Turn off the heat and add in butter, vanilla and whisk until smooth.
If there are lumps you can run it through a mesh strainer.
Place in the refrigerator for 3-4 hours until cool and thickened.
