Start this recipe by melting together 100g margarine with 100g chocolate. Finely blitz 100g of the hazelnuts and add to the mixture. Coarsely chop the remaining 75g and put aside. Meanwhile, whip the 3 egg whites to stiff peaks and put aside. In another bowl, whip together the 3 egg yolks with the caster sugar and orange zest for 5 minutes. Fold in the melted chocolate mixture along with 50g of the coarsely chopped hazelnuts. Next, carefully fold in the egg whites. Chop up 10 of the jaffa cakes and mix in. Line a 7 inch cake tin with baking paper and spoon in the cake mixture. Bake in the oven at 180°C for approximately 40-45 minutes. Allow to cool, then pour over the heated chocolate spread and decorate with the remaining 25g hazelnuts and more crumbled jaffa cakes.