For the dark chocolate mousse: Pour the cream into a bowl and beat with an electric beater till the cream fluffs up and forms soft peaks. Keep aside.

Put the chocolate pieces, butter and cocoa powder in a bowl and melt the chocolate over hot water. Once the chocolate has melted, whisk (by hand) the mixture so it is blended. Add the 5 tbsp water and continue whisking till the chocolate mixture is smooth. Take off the heat.

Adding water to the chocolate here will not cause it to seize. The butter added to the chocolate will ensure this. Normally, unsalted butter is used in most desserts. It is difficult for me to find this here. I also find that the salt in the butter balances out the extra sweetness in most desserts.

Now add the beaten cream and the vanilla essence and slowly fold in the cream into the chocolate mixture till well blended, trying to keep as much of the fluffiness in it as possible. Pour into 6 glasses and chill in the fridge.

Make the white chocolate mousse similarly, adding orange juice and orange zest. White chocolate is usually sweeter, but the tang of the orange juice reduces the sweetness, so I added 1 tbsp of sugar here to adjust for that. You may choose to leave out the sugar.

Add the orange essence to the cream and make the mousse as above. Pour the orange mousse over the chocolate mousse in the glasses. Chill for at least 5 to 6 hours. Decorate as desired and serve.