1.Preheat oven to 150°C. Grease a deep 20cm round cake pan; line base and side, extending baking paper 5cm above side.
2.Make cake according to directions on packet. Spread mixture into pan and bake about 1¼ hours. Stand cake in pan 5 minutes; turn, top-side up, onto wire rack to cool.
3.Knead ready-made icing on surface dusted with sifted icing sugar until icing loses its stickiness. Tint icing green; divide icing into three equal portions.
4.Roll one portion of icing between sheets of baking paper into an oval shape, large enough to wrap around an ice-cream cone. Brush a cone with jam and wrap cone in icing. Repeat with remaining cones, jam and icing. Drizzle each cone with chocolate; top cones with silver cachous.
5.Level top of cake. Place cake, top-side down, on a 30cm prepared round cake board and secure with a little frosting. Spread frosting all over cake. Position cones, chocolates and cachous on cake before frosting sets.
6.Just before serving, dust cake with sifted icing sugar.
7.In a small saucepan, combine sugar and water; stir with a wooden spoon over high heat, without boiling, until sugar dissolves. Boil, uncovered, without stirring, about 3 to 5 minutes or until syrup is slightly thick. If a candy thermometer is available, the syrup will be ready when it reaches 114°C.
8.Meanwhile, in a small bowl, beat egg whites with electric mixer until stiff; keep beating (or whites will deflate) until syrup reaches the correct temperature.When syrup is ready, allow bubbles to subside then pour a very thin stream onto the egg whites with mixer operating on medium speed. If syrup is added too quickly to the egg whites, frosting will not thicken.
9.Continue beating and adding syrup until all syrup is used. Continue to beat until frosting stands in stiff peaks (frosting should be barely warm by this stage).
The cake and ice- cream cones can be prepared one day before the party. The frosting is best spread over the cake about an hour before serving. The frosting will lose its gloss after an hour or so.Note