1
Grease and line a 20cm round cake tin with baking paper.
2
Combine dark chocolate with butter in a medium saucepan. Don't heat yet.
3
Combine instant coffee granules with cold water, then pour the mixture into the saucepan.
4
Heat gently until all ingredients are melted, being careful not to overheat.
5
Separately, combine self-raising flour, plain flour, bicarbonate of soda, light muscovado sugar, golden caster sugar, and cocoa powder, making sure to remove any lumps.
6
Preheat the oven to 160°C.
7
Mix eggs with buttermilk until combined.
8
Add the melted chocolate mixture and egg mixture to the flour mixture, then blend everything together until smooth and somewhat liquid in texture.
9
Pour the batter into the cake tin and bake for approximately 1 hour and 25 minutes. To check if it's done, insert a skewer in the center – it should come out clean and the top should feel firm.
10
Allow the cake to cool in the tin then remove and place on a wire rack to cool fully. Once cool, slice the cake horizontally into three layers.
11
For the ganache filling, place dark chocolate into a bowl. In a pan, heat double cream with golden caster sugar until it is almost boiling.
12
Remove from the heat and pour the cream and sugar mixture over the chocolate. Continue stirring until the chocolate is fully melted and the mixture is smooth. Allow it to cool until slightly thicker but still easy to pour.
13
Layer the cake with a thin spread of ganache, then pour the remaining ganache over the top and let it cascade down the sides. Use a knife to fill in any gaps and achieve a smooth finish.
14
Grate milk chocolate on top for decoration.