Preheat your oven to 190C / 375F / Gas Mark 5 and prep you muffin tins with cases.
Cream the butter and sugar together until it is light and fluffy. Add the eggs one at a time beating in-between each addition. Make sure everything is well incorporated.
In a separate bowl, stir together the cocoa powder; food colouring and vanilla extract to make a paste. Because I used a gel colouring instead of a liquid colouring I found there wasn’t enough liquid to mix this to a paste so took a tablespoon out of the buttermilk and this made it into a paste for me.
Add your red chocolaty paste to your batter and mix well until everything is really well mixed together.
Sift the flour and salt together into a separate bowl and add a 3rd of it to the batter and mix. Then add half the buttermilk and mix. Then another 3rd of the flour, mix then the final amount of buttermilk again mix then the final 3rd of flour. Make sure everything is well mixed together.
In another small bowl mix the vinegar and baking soda together and add this to the cake batter and mix it in by hand until fully incorporated.
Spoon the batter into your paper cases and place them in the centre of your oven for 18-20 minutes. Bake them until they are firm to the touch. Take them out of the oven and allow them to cool in their tins for 5 minutes then transfer them to a wire wrack to fully cool down