Place milk, water, sugar and salt in a saucepan and heat over medium heat.
In a bowl, whisk cacao powder with 4 tbsp of water until lumps free then pour into the milk mixture and stir.
Add in the chocolate and stir until dissolved.
Place agar agar in a glas, add in 1 tbsp of water, stir and pour into the chocolate mixture.
Bring the mixture to a boil, then boil for 1-2 minutes.
Pour the mixture into a mold, let it cool completely before placing in the fridge. Let it rest in the fridge for a couple of hours before serving.