Preheat the oven to 180 degrees C and grease two 23cm round cake tins. Line the bottom of the tins with baking paper and grease the paper, then dust with flour.
Sift together the flour, sugar, cocoa, bicarb and salt into a mixing bowl. In another bowl, beat the eggs then add the sour cream and vanilla and beat until smooth.
With an electric mixer, mix the melted butter and oil. Add the cold water and mix. Add the flour mixture all at once and mix 1 minute. Add the eggs and mix another minute until well blended. Divide between the cake tins.
Bake cakes for 40 minutes or until they test done.