Pre-heat the oven to 160C(320F) fan-forced and grease and line two 20cm round cake tins.

In a large saucepan, combine the butter, chocolate, sugar, water, golden syrup and vanilla extract and stir it over medium heat until everything melts and comes together.

Set the mixture aside to cool for 20 minutes.

One at a time, whisk in the eggs and then sift in the flours. Whisk them through until the mixture is smooth.

Divide it evenly between the two tins and bake the cakes for 40-50 minutes or until a cake tester inserted in the middle comes out clean.

Leave the cakes to sit in the tins for 20 minutes before turning them out on to a wire rack to cool completely.

To make the icing, put the water, 30g dark sugar and 175g butter in a pan over a low heat to melt. When the mixture begins to bubble, take the pan off the heat and add the chopped chocolate, swirling the pan so all the chocolate is heated. Leave it for a minute or two and then whisk until the icing turns smooth and glossy.

Nigella says to leave it for about an hour whisking every now and then. Mine took at least 2 hours to thicken significantly.

Place a small blob of icing on your serving plate and invert one of the cakes on top of it. Cover the cake with icing and put the second cake on top, right-way-up. Coat the top of it with icing.