As terrible as it may sound (I can already see the expression of pure horror depicted on your faces), this is actually a recipe derived and passed down from the time when nations were at war, food supplies were scarce and people had to be inventive. If we don’t consider the commercial recipes readily available on our supermarket shelves, mayonnaise mostly comprises egg yolks and oil, which provide the necessary fats to this cake without having to use any added butter. And yes, while it’s extremely easy to simply grab a jar of mayonnaise, if you want to be perfectly sure your cake doesn’t contain any nasty chemicals or unwanted salt/vinegar/pepper (you name it, it’s probably there), then you should make your own mayonnaise.
That said, a commercial variety would do just fine. This recipe comes from the Serious Eats food blog, which in turn derived the sour cream frosting from another blog. I have amended the frosting recipe anyway, but what follows is merely the translation (from US measurements) of the above recipe. This cake is moist, soft and crumbly and will keep for quite a long time without drying out. The frosting is rich and luscious and, contrary to what you might think, is really tastes of chocolate and is not excessively sweet.
Ingredients (for the cake)
- 3 large eggs
- 340g golden caster sugar
- 1 tsp vanilla extract
- 280g plain flour
- 1/2 tsp baking powder
- 1/2 tsp bicarbonate of soda
- 90g cocoa powder
- 1/2 tsp salt
- 315ml recently boiled water
- 312ml mayonnaise
Ingredients (for the frosting)
- 430g dark chocolate, roughly chopped
- 2 tsp espresso coffee
- 560ml sour cream, at room temperature
- 50g unsalted butter, softened
- 150ml golden syrup
- 1 tsp chocolate extract
- Start by greasing and lining the bottom of 2 x 20cm deep cake pans with baking parchment. Pre-heat the oven to 180C.
- In the bowl of a freestanding mixer, combine the eggs and sugar and whisk on high speed for at least 5 minutes until the mixture is pale, foamy and has doubled in volume.
- Switch the attachment to the palette/leaf one, add the mayonnaise and vanilla extract and combine thoroughly.
- In a bowl, sift the flour, raising agents, cocoa powder and salt, then add it to the wet ingredients. Combine thoroughly on low speed, scraping the bottom of the bowl from time to time. The mixture will be fudgy and rich at this point.
- Last, slowly pour in the water with the motor running and ensure the mixture is evenly combined. Scrape the bottom of the bowl to disperse the ingredients. The mixture will be very runny, but this is normal.
- Divide the batter evenly between the two tins and bake for about 30 minutes. Check with a skewer the sponges are cooked through, then transfer to a wire rack to cool completely.
- To make the frosting, melt the chocolate and butter in a heavy bottomed saucepan over a gentle heat, then add the espresso, whisk together and set aside to cool slightly.
- In a bowl, combine the sour cream, chocolate extract and golden syrup, then add to the melted chocolate (now at room temperature) and gently whisk to combine. The frosting will turn a lighter shade of brown and will be very soft and whipped.
- Cover with clingfilm and refrigerate for at least 20 minutes. This will slightly harden the frosting and make it easier to spread. If the icing gets too hard, remove from the fridge and leave at room temperature to soften again.
- To assemble the cake, place one of the cooled sponges onto the plate/serving dish of your choice, then spread approximately one third of the frosting on top, making sure to get right to the edges. Dollop another third of the icing on top and spread that evenly, then gently ease the remaining frosting around the sides and spread using a palette knife to ensure a smooth finish. I have decorated the cake on top by scraping the icing in a whirlwind-like pattern and placing a chocolate in the middle, but you can choose to keep the cake very plain.
- Just a suggestion: this cake is delicious with a cup of fruit tea and some cream poured on top. Enjoy!