Add the cream, butter & golden syrup into a medium sized saucepan then set over a low heat & warm, stirring frequently until the butter has melted & the cream is steaming hot. But not boiling! If you take the temperature of the cream, it will be around 80°c/176°f when ready.
Whilst the cream is warming up, chop the chocolate into small pieces then place into a heatproof mixing bowl, along with a pinch of sea salt.
Once the cream is hot, pour it over the chocolate then let the mix stand for 2 minutes, without stirring.Don't skip this step! Letting the mix stand melts the chocolate more evenly. Next, use a spatula to gently stir the cream & chocolate together until melted & smooth, starting from the middle, working outwards.
Once the chocolate has melted, add in the mascarpone then use a stick blender to blend it into the ganache. The mix may look split at first but keep blending & it will come together, to make a smooth, shiny ganache.
Transfer the ganache to a shallow dish then cover the surface with a piece of clingfilm & leave to set at room temperature until thick enough to spread. This will take an hour or two. You can speed this process up by putting the ganache in the fridge but it will lose some of its' shine!
Give the ganache a stir just before using, to make it more spreadable.As the ganache contains mascarpone, it will need to be stored in the fridge if you're making it ahead of time. To make it more spreadable after being chilled, you'll need to let the ganache sit out at room temperature for around an hour.