Ingredients (all at room temperature):

Makes 1 x 8” cake or 24 cupcakes. See my handy table at the bottom of the page for other yields.

-200g salted butter
-500g caster sugar
-4 Eggs 
-1 tbsp red food colour paste
-400mls Buttermilk or 1 + 2/3rds tbsp of vinegar or lemon juice added to the same amount of whole milk and left to stand for 10 mins)
-1 + 2/3rds tbsp vanilla extract
-500g Plain flour
-35g Cocoa powder
-1 + 2/3rds tsp Bicarb soda 
-5tsp Vinegar

You will also need:

-Freestanding electric mixer or handheld electric whisk
-3 x loose bottomed sandwich pans or 2 x 12 hole muffin tins and 24 muffin cases
-Bake even strips (optional, see post)
-Pencil
-Scissors
-Grease proof paper
-Cake release spay/butter and flour, for greasing
-Large icecream scoop (I recommend no.16 Sunnex brand) or spoons if you’re making the cupcakes
-Cooling rack

*Just to let you know: I only recommend products I use myself. The list above may contain affiliate links from which I earn a small commission. 

Method:

Preheat the oven to 170°C/325°F/gas mark 3.

- Put the butter and the sugar in a freestanding electric mixer with a paddle attachment (or use a handheld electric whisk) and beat on medium speed until light and fluffy and well mixed. Turn the mixer up to high speed, slowly add the egg, vanilla extract and beat until everything is well incorporated.

- Add the red food colouring and and mix thoroughly until evenly combined and coloured (scrape any unmixed ingredients from the side of the bowl with a rubber spatula). Turn the mixer down to slow speed and slowly sift in half the flour and all of the cocoa powder.

- Beat until well mixed, then pour in half the buttermilk and beat until everything is well incorporated. Repeat this process until all the flour and buttermilk have been added. Scrape down the side of the bowl again. Turn the mixer up to high speed and beat until you have a smooth, even mixture. Turn the mixer down to low speed, combine the bicarbonate of soda and vinegar in a teacup or similar sized bowl and as soon as it starts fizzing up pour into your red mixture.  Beat until well mixed, then turn up the speed again and beat for a couple more minutes.

- Spoon the mixture into the cupcake cases or cake tins until two-thirds full and bake in the preheated oven for 35-45 minutes for cake layers or 20-25 minutes for cupcakes. Turn everything 2/3rds of the way through to ensure they bake evenly and non of the edges burn. 

- 5 minutes before the baking times up, open the oven a crack to check on them. Unlike most cakes I find the sponge doesn’t necessarily bounce back when touched and if it does you’ve likely over done it. Poke the sponges and if the bottom 2/3rds feel spongy then you’re on the right track. Insert a knife, look for a ‘cakey’ fudgey texture. A few crumbs should stick to the knife when it comes out but you certainly don’t want it molten inside, if that’s the case put it back in. The difference between runny and fudgey at this stage can be a few minutes though so don’t go far- your cake needs you right now! 

- When you’re happy, take your sponges out the oven. If making cupcakes, turn them out onto a cooling rack as soon as soon as possible (If left to cool in the tin, you risk the cases steaming off). If you’re making cake layers, leave to cool for 20 minutes before removing them from the tin to cool slightly. If done right, your cakes should shrink and ‘deflate’ a little, so don’t be disheartened when that happens- they are going to taste really good. Wrap in clingfilm while still slightly warm to the touch, once they’ve cooled completely, transfer to the fridge or freezer.