Preheat oven to 160*.

Grease a deep baking tray.

Pour the water into a small saucepan and bring to a boil.

Add the butter and oil to the water and stir until the butter has melted completely.

Remove from heat and set aside to cool.

In a separate bowl, sift the flour, cocoa powder, baking powder and sugar together.

Add the water mixture to the dry ingredients and mix well.

Add the eggs and milk and mix.

Pour the cake batter into the prepared baking tray and bake for about 1 and a half hours, or until a test skewer inserted in the centre comes out clean.

Remove from the oven and set aside to cool.

To decorate: melt the chocolate in a steel bowl suspended over a saucepan of simmering water and then combine with the cream.

Pour the chocolate ganache over the cake and smooth out with a spatula.