Line a slice tray with baking paper. Crush biscuits roughly using a rolling pin or food processor then combine in a medium size bowl with chopped pistachios, coconut, sugar and cocoa. Set aside.
Place butter, chocolate and syrup in a saucepan over low heat. Stir for 3-4 minutes or until melted and smooth. Remove from heat and allow to slightly cool before whisking in the egg.
Add chocolate mixture to the biscuit mix and stir to combine. Transfer mixture to prepared pan. Using the back of a spoon, press mixture evenly into pan. Cover and refrigerate until firm.
Make chocolate topping: Place chocolate and butter in a heatproof bowl over a saucepan of simmering water. Stir until smooth then spread over slice. Refrigerate for 2 hours or until set.
Using a hot knife, cut slice into small sized squares. Then serve.