Melt the chocolate gently over a bain-marie together with the cocoa powder. Put the water and sugar in a small sauce pan and cook until it reads 120⁰c on a thermometer. Meanwhile whisk the yolks until pale and creamy; slowly and carefully pour in the sugar syrup.Continue whisking until mixture cools is cool (approximately 3 minutes) Fold in the chocolate mixture, tangerine zest and whipped fresh cream. Roughly crush the amaretti biscuits and scatter them in the bottom of an 8 inch cake ring. Pour the chocolate marquise over and refrigerate for minimum 3 hours to set. Dust with cocoa powder andgarnish with chocolate decorations and berries.