Having maintained for a long time that I couldn't see the point of adding beetroot to a chocolate cake, my curiosity finally overcame my reticence and I decided to try a recipe.
The first problem was finding a reliable recipe; there are so many variations between those online - is it best to add cocoa or drinking chocolate, cooked or raw beetroot? Should I choose a recipe which also added melted plain chocolate; if so, how much? Prompted by a thread on the BBC Food Messageboards, I decided that I needed a recipe which used cocoa and chocolate together for the best possible flavour. Using raw beetroot seemed more convenient - why add an extra time consuming process? Eventually I settled on this recipe from Delicious magazine, mainly because it added a lot of chocolate and a large quantity of beetroot, so would be a good test of it's effects, but I took a tip from a similar recipe and used 80g flour and 25g cocoa instead of 100g flour. For my own convenience I used an 8" square tin rather than the 9" diameter round tin suggested in the recipe.
The recipe worked very well; I had no problems and the cake baked in the specified time.
Once it was cold, I added my own fudge frosting recipe, as I didn't have any sour cream. This was: 50g plain chocolate, 225g icing sugar, 50g butter and 3 tablespoons of milk melted and combined to a smooth mixture in a saucepan. The frosting is beaten frequently as it cools and thickens, until it is a spreadable texture, then put on top of the cake, spread to the edges and swirled with a knife blade to give an attractive finish - much easier than trying to get a smooth finish!
The cake was a revelation to me - the texture was rich and moist without being too dense and the flavour was deep and chocolatey (not surprising with 250g chocolate in it) but not oversweet. I couldn't taste the beetroot at all, although the occasional change in texture reminded me that there was grated vegetable in there!
I guess the conclusion for me is that I wouldn't buy beetroot especially to make a chocolate cake, but when there's a summer glut to be used, it does make a well-textured, tasty cake.