Break the chocolate into a heatproof bowl and add the double cream. Slowly heat over a pan of gently simmering water, stirring occasionally, until all the chocolate has melted and combined.
Remove the bowl from the heat and leave to cool at room temperature until it reaches a spreadable consistency.
Whilst the chocolate is cooling, place the jam in a bowl and gently warm. This can be done either in the microwave or in a small pan on the hob - be wary not to overheat. We just want to make it spreadable.
Evenly spread the jam across the base of each cake, right to the edges.
Once the chocolate ganache has cooled to a thick enough consistency to spread, you're ready to assemble! Using a small palette knife, take one sponge and spread a generous amount of ganache on top of the jam. Sandwich the two sponges together.
Finally, using your palette knife, spread the rest of the ganache over the top of the cake. Add some chocolate shavings for decoration. Enjoy!