In a metal pan, soak Gelatin with water and keep aside for 15 mins.
Combine cocoa and corn flour, custard powder in 1 cup Milk and keep aside.
Boil rest of the milk along with sugar in a shallow milk pan. Add the cocoa mixture to it and stir continuously. When it gets the soup consistency turn off the flame.
Now heat the soaked Gelatin water till it's dissolved completely and starts too thick (3-5 mins in medium flame). Combine this with cocoa milk mixture.
Add condensed milk, cream and vanilla essence at this stage. Combine well and pour immediately into pudding dish/ individual glasses/ moulds.
Let it cool and transfer to the lower rack in refrigerator for 1 hour. Cover the pudding dish to prevent drying.
Top the mousse with chocolate syrup/ chipped kiwi fruit/ chopped strawberry / raspberry/ chocolate shavings or whipped cream.