Preheat oven to 350 degrees and line a cupcake pan with paper liners.
In a medium bowl, combine flour, baking powder, cinnamon and salt. Set aside.
In a stand mixer or in a large bowl and a hand mixer, cream together butter and brown sugar for about 4 minutes, until light and fluffy on medium/medium high speed.
Add the egg, mixing well and scraping the sides of the bowl.
In a small bowl or pourable measuring cup, whisk together milk and vanilla. Set aside.
Starting with the dry ingredients, add about ⅓ to the butter mixture and beat until combined.
Add half of the milk and mix well. Continue alternating dry and wet ingredients, ending with the dry ingredients.
Pour batter into each cupcake liner filling about ⅔ full. Bake for about 16 minutes or until a toothpick inserted in the middle of the cupcake comes out clean.
Let cool in the pan for about 10 minutes and then transfer to a wire rack to cool completely.