To make the cupcakes: Preheat the oven to 325f / 170c. 

Put the butter and sugar into a large bowl, or the bowl of a freestanding mixer. Using the paddle attachment on the mixer, or a handheld electric mixer beat the butter and sugar on medium speed until light and fluffy (about 2 minutes). Crank the mixer up to high and slowly add the egg until well mixed. 

In a separate small bowl mix together the cocoa powder, red food colouring and the vanilla extract to make a thick, dark red paste. Add the paste to the butter mixture and mix thoroughly until evenly combined. With the mixer on low speed, add half of the buttermilk and beat until well mixed. Add half of the flour and beat until incorporated. Add the other half of the buttermilk, and mix. Finally, add the last half of the flour and mix again. Scrape down the sides of the bowl and with the mixer on medium or high beat until everything is well-mixed. 

Now, with the mixer back on low add the baking soda and the vinegar. And again turn the mixer up and beat for a minute to make sure everything is really well incorporated. 

Spoon the mixture into paper cases - be sure to fill them only to the 2/3 mark. This seems quite low, but they do rise quite a bit and the frosting recipe makes a ton so you need a little bit of extra space for a big glob of frosting. Bake 20-25 minutes or until the sponge springs back when touched. Let cool in pan for 3 minutes, then allow to cool completely on a wire rack. 

To  make the frosting: Beat the confectioner's / icing sugar and butter together in a freestanding mixer, or with a handheld mixer on medium or low speed until the mixture comes together. Add all of the cream cheese at once and turn the mixer up to medium-high. Beat the frosting until it is light and fluffy - at least 5 minutes. But do be careful not to over-mix as the mixture can quickly split and become runny. 

When the cupcakes are cold, spoon the frosting on top and swirl around with a pallet knife. 

Makes 12 cupcakes, and enough frosting to cover 12 cupcakes generously.