Place 3/4 of the amaretti biscuits into a food processor with the toasted almonds and cocoa and blitz together to crush. Stir in the melted butter. Press this mixture into the base of a lined springform cake tin. Next, place the ricotta into the food processor (no need to clean the bowl) and blitz. Add in the amaretto liqueur, vanilla, icing sugar and orange zest and blitz again. Finally, blitz in the melted dark chocolate until you have a smooth chocolate mousse. Spoon this mixture over the amaretto base and even out. Place in the fridge for 3 hours or overnight to set. To serve, remove from the tin and decorate the top with the remaining amaretti and extra chocolate and almonds.