Hummingbird Bakery chocolate cupcakes

My daughter turned 15 last week. Every year I say no more parties and every year so far I have given in. This year she invited her friends around to the house, they just hung out, sang and danced. They set themselves up with a homemade photo booth and took loads of great photos. Considering there were 26 girls, they were a pleasure to have. I kept the pizzas coming and made about 37 cupcakes. I think there were four left at the end of the night. The Hummingbird Bakery cupcake recipes are definitely my recipe of choice. I started off by putting too much mixture in the tin and they were too large, and I didn't have enough mixture to make a dozen. The mixture should make a dozen as they do rise considerably. 

Ingredients
Makes 12
100g plain flour
20g cocoa powder
140g caster sugar
1½ tsp baking powder
a pinch of salt
40g unsalted butter, at room temperature
120ml whole milk
1 egg
¼ tsp vanilla extract

Method
Preheat the oven to 170°C
Put the flour, cocoa powder, sugar, baking powder, salt and butter in a freestanding electric mixer with a paddle attachment (or use a handheld electric whisk) and beat on slow speed until you get a sandy consistency and everything is combined.
Whisk the milk, egg and vanilla extract together in a jug, then slowly pour about half into the flour mixture, beat to combine and turn the mixer up to high speed to get rid of any lumps.
Turn the mixer down to a slower speed and slowly pour in the remaining milk mixture (scrape any unmixed ingredients from the side of the bowl with a rubber spatula). Continue mixing for a couple more minutes until the mixture is smooth. Do not overmix. Divide the mixture between the cup cake cases filling to about ⅔ full and cook for 20-25 minutes. They should spring back when touched.

Chocolate frosting
300 g icing sugar, sifted
100 g unsalted butter, at room temperature 

40 g cocoa powder, sifted
40 ml whole milk

Beat the icing sugar, butter and cocoa powder together in a freestanding electric mixer with a paddle attachment (or use a handheld electric whisk) on medium-slow speed until the mixture comes together and is well mixed.
Turn the mixer down to slow speed. Add the milk to the butter mixture a couple of tablespoons at a time. Once all the milk has been incorporated, turn the mixer up to high speed. Continue beating until the frosting is light and fluffy, about 5 minutes.
The longer the frosting is beaten, the fluffier and lighter it becomes.