Grind or crush the biscuits. Melt the butter and mix it with them in a bowl. Put the mixture in a cake form and press down on it with your fingers. Crumble the chocolate and melt it in a water bath.
Beat the confectionery cream, while gradually adding the powdered sugar. To the cooled chocolate, add the cream in 3 lots, while stirring with a spatula. Prepare the gelatin according to packet directions.
Add it to the cream and stir. Pour the mixture onto the biscuit layer and put the cake in the fridge for at least 4 hours.
Once the cake hardens, slide a knife along the inside of the walls and release it from the ring. I crumbled a few hazelnuts for decoration.