Place some baking paper into the bottom of a square slice tin , leaving two of the ends over laying with baking paper a little and set aside till needed .

Process the butternut biscuits until fine crumbs .

Melt the butter

Place the biscuits into a bowl and add the vanilla sugar and the melted butter and mix till well combined

Now place the prepared biscuit mixture into the base of the prepared slice tin spreading it evenly all over the tin base . Then set in the fridge to set whilst you prepare the mousse mixture .

Place the cream into a large , clean , dry bowl and whip till soft peaks form .

Brake all the chocolate up and place in a large heatproof bowl and melt , either by microwave in short busts stirring after each burst , or , over a pot of simmering water , until the chocolate is melted and smooth , let cool slightly .

Now gently fold the whipped cream into the melted chocolate in two batches until will combined . This May take a little elbow grease as the chocolate tries to set .

Once chocolate cream mix is combined , pour it over the prepared base biscuit crumbs in the slice tin , evenly all over the top . Then place in the fridge to set for at least an hour .

Once set , remove from the fridge and carefully slide slice out of the slice tin , using the baking paper to help it lift out . Then using a long sharp knife , cut the slice lengthwise a few times , then turn and slice lengthwise again creating little squares slices . Keep refrigeratorated until ready to serve .

Dust with cocoa powder and serve with cream and toppings of your choice . Enjoy . :-) .