Chop hazelnuts in a food processor. Toast lightly in a dry frying pan and set aside to cool.
Beat egg whites with an electric beater until foamy. Add cream of tartar and salt and continue beating until stiff.
Mix together icing sugar and castor sugar.
Slowly add to the whites until a quarter is left. (Beat well after each addition.)
Mix cornflour with remaining sugar and fold into the whites, with the vanilla essence.
Measure off two quantities, 150ml each, of meringue, and colour one quantity green and the other mauve û a drop each of red and blue.
Line two baking trays with foil and trace two circles, using the base of your 23cm-diameter baking pan as a guide.
Spread a thin layer of white meringue over each circle and sprinkle with the hazelnuts. Pipe stars onto the foil, using the mauve and left-over white meringue, then pipe leaves, using the green meringue.
Bake meringues in a preheated oven for one hour. Switch off oven and leave meringues in it until cool and crisp.
Heat cream and add chocolate. Mix until smooth. Refrigerate until cool and, just before assembling the cake, beat the ganache until thick, using an electric beater.
Once meringues have cooled, remove them from the oven. Preheat oven again, to 180 ¦C.
Lightly grease two 23cm-diameter, loose-bottomed cake tins and set aside.
Sift together dry ingredients. Beat together oil, 125ml hot water, egg yolks and essence and mix into the dry ingredients until just combined. Beat egg whites to form soft peaks and gently fold into batter mixture.
Pour into cake pans and bake in preheated oven for 30 minutes, or until a skewer inserted comes out clean.
Cover the sides and top of one cake layer with half the chocolate ganache.
Top with a meringue circle and spread with half the whipped cream. Add the second cake layer, coat with remaining ganache and place other meringue circle on top.
Spread with remaining cream.
Decorate the top with flowers and hazelnuts and the sides with the smaller meringues.