For the cake base:

1. Sift all purpose flour, cocoa powder, powdered sugar, baking soda, baking powder and salt in a bowl.
2. Beat egg, milk, oil, vanilla and water in a bowl and add it to the flour mixture. Beat until smooth and well combined.
3. Preheat the oven to 210 deg C.
4. Grease 8-inch round springform pan with butter and dust with flour.
5. Pour the batter into the pan and bake for 20-25 mins at 210 deg C.
6. Check if cooked by inserting a tooth pic in the center.
7. Once done, allow it to cool on a wire rack for a while.

For the mousse:

1. Chop the dark chocolate and 125 gms of butter into small chunks.
2. Melt it using a double boiler or on a bowl over a pan of hot water. Once it melts and becomes a smooth mixture, remove from flame and keep it aside for it to come to room temperature.
3. Take a bowl full of ice cubes.
4. Place another bowl on top of the ice and drop in 100 ml of whipping cream in it.
5. Add 1/4 cup of sugar to the cream if the cream is sugarless.
6. Beat well until stiff and fluffy.
7. Take 2 tsp of gelatin in a microwavable bowl and add 2 tsp of water to it.
8. Microwave for 30 seconds or until it melts.
9. Allow it to come to room temperature.
10. Pour in half of the melted butter chocolate mixture into the cream and fold in gently.
11. Add the remaining chocolate mixture and fold too.
12. Finally pour in the gelatin mixture and fold until it combines well.
13. Fill this mousse mixture into a large piping bag.
14. Pipe a 1-inch layer of mousse on top of the cake.
15. Smoothen it with spatula and refrigerate until mousse is set, about 20 minutes.
16. Repeat the same process with milk chocolate to make light chocolate mousse.
17. Pipe it on top of the bittersweet chocolate mousse.
18. Refrigerate at least 4 hours and up to overnight.
19. Decorate on top with chocolate curls or shavings.
20. Remove from Springform pan, slice and serve chill.
21. Enjoy the most sinful dessert.

Recipe courtesy: 4th sense cooking