For the caramel, add the sugar to a medium saucepan and place it over medium heat. Pour the cream into a separate small saucepan, place over a medium heat, bring to a simmer, then remove from the heat.

Cook the sugar until it is fully melted and caramelised to a dark coppery brown colour. Add the butter and salt and swirl to combine. Carefully pour in half the cream; it will bubble up aggressively, so take care and allow the bubbling to subside before pouring in the rest.

Pour the smooth caramel into a large bowl, then set it aside for 30 minutes before transferring it to the refrigerator to chill for at least 4 hours.

To make the ganache, place the chocolate in a large heatproof jug and melt it in the microwave. Pour the cream and golden syrup into a small saucepan, place over a medium heat and bring to a bare simmer. Remove from the heat and pour a third over the chocolate and stir to combine. Add the remaining cream in two additions, stirring well until a silky-smooth ganache is formed. Add the butter and stir it into the ganache until it is smooth.

Preheat the oven to 170°C/150°C Fan (340 ̊F). Lightly grease a 9x13inch cake pan and line the base and sides with baking parchment.

To make the cake, place the butter and chocolate in a bowl set over a pan of simmering water and heat, stirring occasionally, until both are fully melted. Meanwhile, mix together the flours, baking powder, bicarbonate of soda, salt, brown sugar and cocoa.

Remove the bowl of chocolate from the heat and stir in the hot coffee, then the buttermilk. Once smooth, add the egg and whisk until smooth and combined. Pour the liquid ingredients into the flour mixture and briefly whisk until a smooth batter is formed.

Pour the batter into the prepared tin and spread it into an even layer. Bake in the preheated oven for 18-20 minutes or until the cake springs back to a light touch and has just started to pull away from the sides of the tins. Allow the cake to cool for 10 minutes, then use the parchment to lift it onto a wire rack to cool completely.

Remove the caramel from the refrigerator and, using an electric hand mixer, whisk on medium-high speed until the caramel turns light and pale and forms soft peaks.

To assemble, use a serrated knife to cut the cake layer into three smaller rectangles. Place the first cake layer on a serving plate and spread a little of the ganache over it, leaving a small border around the outside edge. Add a third of the caramel and spread it to cover the ganache layer. Repeat this layering process once more before adding the final layer of cake. Spread the remaining ganache over the top and sides of the cake, then set aside until the ganache has set.