For the cake:
250g unsalted butter, at room temperature and cut into 2cm cubes, plus extra for greasing the pan
200g Islands dark chocolate drops (75% or 85%)
1½ tsp instant coffee granules, dissolved in 350ml boiling water
2 large eggs, lightly beaten
2 tsp vanilla extract
240g self-raising flour
30g Islands cocoa powder, plus 1½ tsp, for dusting
¼ tsp salt
For the Islands chocolate ganache:
200g Islands 75% dark chocolate drops
200ml heavy cream
3 tsp golden syrup
3 tsp unsalted butter, at room temperature
For the espresso cinnamon mascarpone cream (optional):
375ml heavy cream
Scraped seeds of 1/2 vanilla pod
2½ tsp finely ground espresso
¾ tsp ground cinnamon
1¾ tbsp icing sugar
1. Heat oven to 170C. Grease a 23-centimetre round springform tin with butter and line with baking paper, then set aside.
2. Make the cake: Place butter, Islands chocolate and hot coffee in a large heatproof bowl and mix well until everything is melted, combined and smooth. Whisk in sugar by hand until dissolved. Add eggs and vanilla extract and whisk again until thoroughly combined and smooth. Sift flour, Islands cocoa powder and salt together into a bowl and then whisk this into the melted chocolate mixture. The batter here is liquid, but don't think you have missed something; this is how it should be.
3. Pour batter into the prepared pan and bake for 1 hour, or until the cake is cooked and a skewer inserted into the centre comes out clean or with just a few dry crumbs attached. The top will form a crust and crack a little, but don't worry, this is expected. Leave the cake to cool for 20 minutes before removing from the pan, then set aside until completely cool.
4. Make the chocolate ganache: Place the Islands chocolate drops in a food processor, process until fine and set aside. Combine cream and golden syrup in a small pan and place over medium-high heat. As soon as bubbles begin to appear (just before it comes to a boil), remove from the heat. Get the food processor running again, with the chocolate still inside, and pour in the hot cream in a steady stream. Process for 10 seconds, then add butter. Continue to process until mixture is shiny and smooth. (You can also make the ganache by hand; just make sure the chocolate is chopped fairly finely before adding the cream mixture. Stir with a wooden spoon until almost melted, then add the butter. Stir again until the ganache is smooth.)
5. Use a rubber spatula to scrape the ganache into a bowl and cover with plastic wrap, with the plastic actually touching the top of the ganache. Set aside until it has set to the consistency you want. If you want a thin layer to spread over the cake, it can be poured over while liquid so that you get an even, light and shiny coating. For a thicker ganache with a spreading consistency, leave it for about 2 hours at room temperature. (The ganache can be stored at room temperature, providing it's not too warm, for 3 days or kept in the fridge for up to 2 weeks. It can also be frozen, although it will lose a bit of its shine when defrosted.)
6. Make the espresso cinnamon mascarpone cream, if desired: Place all the ingredients in the bowl of an electric mixer fitted with the whisk attachment. Beat for 1 to 2 minutes, until soft peaks form.
7. Peel the parchment from the cake and discard. Transfer to a serving platter and spread the ganache, if using, on top of the cake. Slice into wedges, divide the cake among plates and, if using, spoon the mascarpone cream alongside. With or without icing, the cake will keep well for 4 to 5 days in an airtight container.