Preheat the oven to 175 degrees Celsius. Prepare 24-25 cupcake liners.
In a small bowl, place the plain flour, corn flour, baking powder, salt and cocoa powder together. Whisk it with a wire whisk until it's all combined
In another bowl / measuring cup, stir the buttermilk, vanilla extract and red food colouring together.
In a third large bowl, cream the butter using an electric mixer - on low for 30 seconds. Add in the sugar in three portions, beating on medium speed for one minute after each addition and scraping the sides occasionally.
Add in one egg into the butter-sugar mixture. Beat on medium for a minute. Scrape the sides and beat in the other egg. Beat on medium for a minute.
Sift in a third of the flour mixture and fold in gently until all the flour mixture are almost incorporated into the cake batter. Add in half of the buttermilk mixture and fold in until all the liquid mixture has been incorporated. Sift in half of the remaining flour mixture and fold it in. Add in the rest of the buttermilk mixture and fold it in. Fold in the remaining flour mixture. The cake batter will be slightly thick.
Place the baking soda in a small, clean bowl. Add in the white vinegar and watch the chemical reaction! Stir the mixture using a small spoon and add in the mixture into the cake batter. Fold it in until fully incorporated.
Fill the cupcakes to 2/3 to 3/4 full. Bake for 15 - 20 minutes until the top springs back when touched and a skewer inserted into the centre comes out clean. Do not over-bake as the top will darken and you'll lose the red colour top, so check the cupcakes frequently after 15 minutes. Let the cupcakes cool completely before frosting it.
Frosting and Assembly
Place the cream cheese and butter in a large, clean bowl. Beat them with an electric mixer on low for 30 seconds. Sift in the icing sugar and add in the vanilla extract and beat until the icing sugar has dissolved into the frosting. Refrigerate the frosting to let it firm up a little.
Transfer the frosting into a piping bag and pipe onto the cupcakes. Decorate with coloured sugar or sprinkles.
This cream cheese frosting is not very sweet and it's a bit soft to pipe (given the warm temperature here in Singapore). You can choose to add more sugar, but you'll lose the tang of the cream cheese!
NOTES
[1] The original recipe calls for sifted cake flour - meaning measuring the cake flour after it has been sifted - I'm not such a hardworking person and I don't have cake flour in my pantry so I simply substituted it with plain flour and corn flour. Normally the substitute is 1/4 corn flour and 3/4 plain flour to give you cake flour, but I altered a bit - resulting cake is still delicious![2] Hershey's cocoa is natural and hence is acidic. Apparently the natural cocoa is supposed to react with the baking soda to produce carbon dioxide and aids in the rising of the cake. I'm not sure if it's really the case though (need to do some experiments)... If using Varlhona cocoa or any Dutch-processed cocoa, it was suggested to up the baking powder by 1/2 teaspoon to counter for the lack of acidity. In addition, this amount of cocoa gives a slight hint of cocoa in the cake, so if you want a stronger cocoa taste, swap out some of the flour with cocoa - but beware: a higher cocoa content will result in drier baked goods and the cake will be less red - so you may need to up the liquid contents.[3] No buttermilk? No problem! In a cup, add in 1 tablespoon of white vinegar or lemon juice. Top up with enough fresh milk to make 1 cup (250 ml/grams). Stir and let it sit for 10 minutes - buttermilk![4] This amount is about 2 small bottles of food colouring. The next time I bake this I will omit the red food colouring and replace it with buttermilk.[5] Softened means the cream cheese and butter are soft to the touch but still cold - not at room temperature. Let the cream cheese and butter sit out of the refrigerator for 15 minutes to soften.[6] Recipe adapted from Pinch My Salt