Line a small spring form tin (mine was about 17cm) with baking paper on the bottom and sides. Ensure the side of the paper is about 4 cms higher than the sides of the tin.
Slice half lamington sponge into 1cm thick slices and place in bottom of tin, ensuring there is no gaps.
Divide the vanilla ice cream into four even parts.
Take 1/4 of the ice cream and let soften until its easy to mix. Add in 1/4 of the raspberry jelly crystals and mix well. Place in tin on top of the lamington sponge and place in freezer for at least 30 minutes to harden up.
Take 1/2 of the vanilla ice cream and mix in the custard, then add the raspberries and mix gently and quickly. Place half of this mix in the cake tin on top of the raspberry jelly ice cream. Put in freezer. Temporarily place the remainder of the ice cream in the freezer also.
Slice the remaining lamington sponge and arrange on top of the custard ice cream. Remember to fill in all the holes. Layer the remaining custard ice cream on top. Return to the freezer for at least 30 minutes.
Use the remainder of the ice cream and add in 1/4 of the jelly crystals. Mix well and layer on top of the custard ice cream. Leave in the freezer until required but at least overnight.
Bring the cream to the boil in a small saucepan and immediately pour over the chocolate. Mix well and then let cool. Once cool remove the ice cream triffle from the freezer and place on serving plate - if not serving immediately then make sure the plate can fit back in to the freezer.
Spread the ganache over the top of the triffle and then decorate with your chosen toppings. Return to freezer or cut and serve. If you return to the freezer ensure that you remove for about 10 minutes prior to serving or it will be impossible to cut.