Preheat the oven to 180ª.
In a big bowl mix the butter with the sugar until the butter seems whiter.
Now add the eggs and the vanilla extract to the mix.
In another bowl smash the bananas along with the cinnamon.
Pour the mashed bananas in the big bowl and mix well. Then add slowly the flour, the baking powder and the milk.
Put three tablespoon of this mix into each cupcakes form.
Take the cupcakes to the oven for about 15 minutes.
Let them chill… I mean really chill because the frosting will be buttercream based and if you're impatient like me you can end with a melted frosting.