Preheat the oven to 350°F. Line a 12-cup muffin pan with cupcake liners.
In a medium bowl, whisk together the flour, baking powder, baking soda, salt, and cinnamon.
In the bowl of a stand mixer, cream the butter, granulated sugar, and brown sugar until light and fluffy, about 3–4 minutes.
Add the eggs one at a time, mixing well after each addition.
Mix in the vanilla and mashed bananas.
Stir in the sour cream.
Alternate adding the dry ingredients and milk, beginning and ending with the flour mixture. Mix just until combined.
Fill cupcake liners about 2/3 full.
Bake for 18–20 minutes, or until a toothpick inserted into the center comes out clean.
Allow the cupcakes to cool completely before decorating.