Preheat the oven to 170°C and line and grease a 13”x 9” deep cake tin.
Beat the butter and caster sugar together for a few minutes until light and fluffy.
Add the eggs one at a time and beat well.
Sift together the cocoa powder, flour and bicarbonate of soda in a bowl and set aside for a moment.
Mix together the buttermilk and vinegar in a jug.
In alternate turns add the flour and the buttermilk mixtures to the rest of the batter. You should add the flour in 3 additions and the buttermilk in 2 additions, starting and ending with the flour.
Add the food colouring and vanilla extract and mix until the colour is as desired
Pour into the cake tin and bake for 60 minutes or until an inserted cocktail stick comes out clean.
Remove from the oven then rest the cake for 10 minutes before carefully removing to finish cooling onto a wire rack. Once completely cooled, cut a very thin slice of the sponge away and whizz up to cake crumbs in the food processor for sprinkling on the top.
Cream Cheese Buttercream:
Cream the butter until soft then add the icing sugar and mix for about 10 minutes until very light and fluffy.
Add the salt and vanilla and mix again to combine.
Finally beat in the cream cheese until the buttercream is smooth. Swirl onto the finished cake with a palette knife.
*how much red food colouring you use is completely dependent on the brand. Be careful using a very liquid food colouring (like Dr Oetker which is the default red food colouring you can get at most UK supermarkets) as it will affect the consistency of the batter. I love to use Squires Kitchen Professional Food Colour Pastes in my baking as they give excellent deep rich colours and don’t affect the recipe at all.[recipe]*If you don’t have any buttercream to hand then you can make your own if you whisk together 400ml whole milk with 2 tablespoon white vinegar and let stand for 10 minutes before using. To this you can then add the 1½ tablespoons of white vinegar that the recipe requires.