Step 1

Preheat oven to 160C. Grease a deep 23cm springform cake pan and line with baking paper.

Step 2

Place the chocolate, butter, coffee and milk in a heatproof bowl set over a pan of barely simmering water (don't let the bowl touch the water) and stir until smooth and melted. Remove from the heat and set aside to cool completely.

Step 3

Sift flour and cocoa powder into a bowl, then add sugar. Fold into the chocolate mixture with eggs, vanilla extract and sour cream.

Step 4

Pour the batter into the cake pan and bake in the oven for 60-70 minutes until a skewer inserted into the centre comes out with some moist crumbs sticking to it but no raw cake batter. Set aside to cool completely in the pan.

Step 5

For the ganache, place all ingredients in a small heatproof bowl set over a pan of barely simmering water (don’t let the bowl touch the water) and stir until smooth and melted. Cool slightly.

Step 6

Remove the cooled cake from the pan and spread with the ganache, then serve.