In a bowl, mash the bananas until they become a puree. Then add the butter, xylitol and egg and mix.
Gradually add the flour, cornstarch and milk and mix.
Finally, put the cinnamon powder and mix a little more, then add the baking powder.
Bake in cupcake molds for 20 minutes in a 180 degree oven.
To finish you can sprinkle with icing sugar and cinnamon or just cinnamon.