1. Crush the biscuits with a rolling pin until mostly crumbs but leaving some bigger chunks for added texture.

2. Melt the dark chocolate and butter in a saucepan over a medium heat until all lumps have gone. Remove from heat and stir in the biscuit.

3. Push the biscuit down into the bottom of a 8 or 9 inch cake pan until well packed. It is best to use a cake pan with a removable bottom but if you don't have one grease a normal cake pan and cut a long strip of greaseproof and lie across the cake pan to make handles then line with greaseproof paper. The strip will help you lift the moussecake out later once set.

4. Place the base into a fridge for around an hour until set and solid.

5. To make the mousse, separate 3 eggs. Lightly whisk the yolks with a bell whisk until slightly lighter in colour and creamy in consistency, a couple of minutes whisking should do it. Set aside.

6. Whisk the egg whites until stiff peaks in a bowl, once this is done whisk the cream until just before it hits stiff peaks, you want it thick but not quite at stiff peak consistency. Set both aside.

7. Melt the white chocolate in a bowl over a pan of water, gently stir until thoroughly melted. Allow the chocolate to cool for a couple of minutes, until its round about lukewarm.

8. Using a bell whisk, whisk the yolks into the chocolate, it will more than likely go to a thick stodgy consistency, don't worry about it, this is fine.

9. Pour the white chocolate mix into the cream mix and whisk with the bell whisk for a couple of minutes until smooth and silky. At this stage if it goes grainy work fast.

10. Pour the creamy chocolate mix onto the egg whites and with a metal spoon gently fold the mix together, it will go light and bubbly.

11. Pour the mousse mix on top of the biscuit base and place back in the fridge for at least 4 hours, ideally overnight, until the mousse sets.

12. Once set gently remove from the cake pan and serve.