Break the chocolate into small pieces. Put the chocolate in a heatproof bowl,set over a pan of simmering water and leave it to melt.Do not let the water touch the bottom of the upper pan.Only let the water simmer.
Add butter and mix,do not allow it to boil or you may burn the chocolate. Stir until completely melted.Remove from the heat and leave it to cool for 10 minutes.
Divide the whipped cream into three portions.
Now add first portion into cooled melted chocolate and fold it. Then add second part of whipped cream and fold .Now lastly add remaining whipped cream and fold it. You will notice very light and airy texture. Gently fold it using spatula. Do not mix it vigorously, do it slowly and gently.
Pour into individual cups filing the cups half . Making sure you keep enough space for the cheesecake layer. Place in the fridge for 3-4 hours.
Once the chocolate mousse has set. Put the softened cream cheese in a mixing bowl, using a hand mixer, whip it until a bit fluffy, about 1 minute. Add the sweetened condensed milk and whip until well incorporated. Pour on top of the mousse, and refrigerate for another 3-4 hours. Garnish with chopped chocolate and chocolate sauce.