To make the base, crumble 300g of cake onto a baking tray and place in a pre-heated oven at 180 degrees (160 fan, gas mark 4) for about 20 minutes, stirring it occasionally in that time until the crumbs become 'toasty'

Remove from the oven and allow to cool in the tray

Meanwhile place your chocolate and butter in a microwaveable bowl and microwave on high power for 30 seconds. Stir well. If you need to heat it a bit more place it back in the microwave and carefully heat again until melted. If you don't have a microwave, set your bowl over a saucepan of boiling water and melt that way instead.

Pour the cake crumbs into the melted chocolate mixture and stir well to combine

Press the mixture into the base of a springform round tin measuring approx. 20cm in diameter, then place in the fridge to set

While the base is setting make the topping...

Whip the double cream in a large bowl until it is just holding shape (don't over whip or it will be impossible to stir the chocolate in!) then set aside

Melt the topping chocolate in the same way as above then add 2tbsp cocoa and 2tbsp warm water and stir well

In another bowl whip the cream cheese with the white sugar using an electric whisk

Finally add the chocolate and cream cheese mixtures to the cream and beat until well combined

Place the chocolate mixture on top of your prepared base and refrigerate for at least 2 hours until set

Scatter more cocoa on the top just before serving