Combine the chocolate and milk in a microwave-safe bowl and microwave on high for almost 40 seconds at the burst of 20 seconds each.
If required microwave it for few more seconds till it melts completely.
Remove and mix well until no lumps remain.
Sieve the mixture and keep aside to cool a bit.
Take whipped cream in a bowl and mix sugar to it. Fold very gently.
Now add whipped cream in batches in the chocolate mixture gradually and fold gently.
Add the coffee mixture and fold gently.
Keep aside.
Pour this coffee mousse over the earlier prepared and cooled coconut base and spread it gently with a spoon or knife.
Refrigerate for 2 to 3 hours hour or till the mousse sets.
Demould the pie and garnish with castor sugar and cocoa powder.