Nigella Lawson's Double Chocolate Cake 

Cake:

400 grams Sydney Blend
250 grams white sugar
100 grams light brown sugar
50 grams unsweetened cocoa powder
2 teaspoons baking powder
1 teaspoon baking soda
½ teaspoon salt
3 large eggs
142 ml sour cream
1 tablespoon vanilla extract
175 grams unsalted butter (melted and cooled) 
125 ml vegetable/canola/corn oil
300 ml chilled  water

Fudge Icing

175 grams dark chocolate
250 grams unsalted butter (softened) 
275 grams powdered sugar (sifted) 
1 tablespoon vanilla extract

Heat: Preheat the oven to 180°C/350ºF.  Butter and line the bottom of two 20cm / 8 inch sandwich tins.

Mix: In a large bowl, mix together the Sydney Blend, sugars, cocoa, baking powder, baking soda and salt. In another bowl whisk together the eggs, sour cream and vanilla until blended. Using a handheld electric mixer, beat together the melted butter and oil until just blended, then beat in the water. Add the dry ingredients all at once and mix together on a slow speed. Add the egg mixture, and mix again until everything is blended and then pour into the prepared tins. 

Bake the cakes for 50-55 minutes, or until a toothpick comes out clean. Cool the cakes in their tins on a wire rack for 15 minutes, and then turn the cakes out onto the rack to cool completely.

Frosting: To make the icing, melt the chocolate in the microwave - 2-3 minutes on medium or in a bowl sitting over a pan of simmering water.

In another bowl beat the butter until it's soft and creamy and then add the sieved icing sugar and beat again until everything's light and fluffy. Then gently add the vanilla and chocolate and mix together until everything is glossy and smooth.

Sandwich the middle of the cake with about a quarter of the icing, and then ice the top and sides too, spreading and smoothing with a rubber spatula.