Grease deep 20cm round cake pan, cover base with paper, grease paper. Combine chocolate, butter, liqueur, water, sugar and nuts in large bowl; stir in egg yolks. Beat egg whites in small bowl until soft peaks form, fold into chocolate mixture, pour mixture into prepared pan. Bake in moderate oven about 45 minutes or until cake is firm; cool in pan.
Carefully turn cake from pan, place cake onto serving plate. Spread top with orange cream, top with meringue layer; refrigerate 2 hours before serving.
Beat egg yolks, rind and sugar in small bowl with electric mixer until thick and creamy. Gradually beat in juice. Transfer mixture to pan, stir over low heat, without boiling, for about 20 minutes or until mixture thickens. Remove from heat. Sprinkle gelatine over water in cup, stand in small pan of simmering water, stir until gelatine is dissolved, stir into warm orange mixture. Beat cream until soft peaks form, then fold cream into orange mixture; cool.
Cover oven tray with foil, grease foil, dust with a little plain flour, shake away excess flour. Mark a 17cm diameter circle on foil. Beat egg whites, sugar, cornflour and juice in small bowl with electric mixer for about 10 minutes or until sugar is dissolved. Spread mixture over circle. Bake in very slow oven for about 1 1/2 hours or until meringue is dry and firm to touch. Cool meringue in oven with door ajar.