Preheat oven to 150 C. Grease and line the base and side of a 24 cm springform cake tin.

Melt butter in a saucepan on a low heat and add the chocolate, stirring to melt. Add the coffee and water mixture and sugar, stirring to dissolve.

Remove the pan from the heat, stir to combine, and pour into a large mixing bowl. Cool for 5 minutes. Sift the flours and cocoa into the chocolate mixture and stir through. Add the eggs and vanilla and combine with an electric mixer until smooth.

Pour the mixture into the preapred tin. Bake for 1 1/2 hours, or until the cake is cooked through (this is a very moist cake). The top will be crusty and cracked. If you prefer a smoother top, cut a piece of baking paper the size of the cake top and place it on top of the mixture before baking.