I have made Nigella's Old Fashioned Chocolate Cake around 5 times now and use exactly the recipe and the ingredients are not out of date. It always seems to be a little dense. I wondered if it is because I may be over mixing the cake batter? I do not have a food processor. I use a free standing food mixer, and use the tool that scrapes the sides of the bowl whilst it is mixing. I use this rather than the wire whisk which gets a lot left in it after mixing. I use low to medium power for around 8 mins. Can you spoil this cake by over-mixing the batter, and should I use the wire whisk rather the scrape and mix tool? Thanks.
Nigella's Old Fashioned Chocolate Cake (from Feast and on the Nigella website) is made with sour cream. The addition of a liquid, such as sour cream or buttermilk, will affect the texture of the cake and you will find that cakes with additional liquids in the batter will have a slightly denser texture than a Victoria Sponge.
The extra liquid will tend to increase formation of gluten, making a less tender cake, so mixing should be kept to a minimum. The mixer method for this cake involves mixing the dry ingredients with the butter before adding the liquid ingredients. This method can help to reduce the formation of gluten by coating the flour molecules with fat and preventing them for absorbing too much liquid. However 8 minutes of mixing sounds a little too much and you should only really do as much mixing as it takes just to combine the ingredients. It is fine to use the paddle attachment on the mixer but it is best to avoid the scraper tool. We would suggest mixing the dry ingredients and butterr on medium speed until smooth, then adding the liquid ingredients and mixing only until combined. It may also help to partially mix in the liquid ingredients with the mixer and then finish the mixing by hand with a spatula, as this will be gentler and give more control.