Preheat oven to 350 degrees Farenheit.
Place the figs and raisins into a mixing bowl and pour the brandy over them. Leave them for 45 minutes, stirring occasionally.
Whisk together flour, cocoa powder baking soda, and kosher salt in a medium bowl.
In a separate bowl, ½ cup of the brandy used to soak the figs (however much you have left after they've soaked 45 minutes), milk, sugar, egg, ½ cup of melted butter, and vanilla until pale.
Pour the wet ingredients into the dry, whisking until no lumps remain. Set aside.
To make the caramel:
Place a frying or sauté pan over moderate heat and add the remaining ½ cup of brandy that was used to soak the figs and raisins, leaving the fruit behind in the bowl, then add the sugar. Bring to a boil and leave to form a think caramel. Remove from the heat, cut the remaining 4 tablespoons of butter into small cubes and stir into the caramel.
Poor the caramel into the base of a springform pan. Place the plumped-up figs on the base of the tin in a single layer, then scatter the raisins using them to fill in any gaps between the figs.
Pour the chocolate cake batter over the fruit and caramel.
Bake in the pre-heated over for about 35 minutes, until a toothpick inserted in center comes out clean, let cake cool for 5 minutes then run a small sharp knife around edges. Place a plate on top of the cake pan and invert. Take side off and slowly lift the cake pan away.