The ganache is made of whipping cream (35% fat) and chocolate (if too high a fat content is used the ganache will split). For the ganache we used Callebaut Finest Belgian 811 Dark Chocolate, (which comes in chocolate drops as opposed to squares).
The ratio of chocolate to cream is 1:1 – we used 200g of chocolate to 200g of whipping cream.
For the heating of the cream, you just need enough to bring the cream to the boil, then take it off and pour over the chocolate drops straight away.
Before pouring the ganache on the cake, tap the side of the container until there are no visible air bubbles.
The ganache will dry on to the cake in approximately five minutes.
The chocolate for the petals must be tempered – this can be done in a variety of ways, but the easiest can be seen here and is done using a microwave. http://www.callebaut.com/uken/techniques/tempering/tempering-in-the-microwave
For the yellow petals, you can use any yellow oil-based, fat-based or powder-based colouring (do not use a water-based food colouring as the chocolate will seize and go thick). Each of these will need a different amount, so add a little bit at a time until you get the colour you want – you can add more colouring in, but it is hard to take away.
They go through exactly the same process as the curled petals, but are left to set straight.
The chocolate is put on strips of acetate using a normal palette knife. The yellow petals are left to dry straight, the brown curled petals are put in a short piece of guttering, sawn in half, to dry. The chocolate only takes 2-3 minutes to dry solid in both cases.
Callebaut buys the acetate strips from Keylink. Alternatively, you don’t have to buy the strips – chefs/bakers could cut up their food-grade plastic bags into strips and use that, or use silicon paper.
The centre of the flower is made from chocolate drops put in a blender for 20 seconds and then pressed into a dome shape so they hold together (we used the tray of a chocolate box).
The chocolate does not need to be refrigerated as it doesn’t have any filling in it, but it should be stored in a cool place in an airtight container. If it is kept out in the light, the colour will start to fade over time – the shelf life of white chocolate is 12 months, so the flower could safely be kept that long before serving.