Preheat oven to 300 degrees F. Add cupcake liners to a 12 serving cupcake pan, and set aside.
In a medium mixing bowl, whisk together flour, baking powder, cinnamon and salt. Set aside.
Add butter to a large mixing bowl, and beat with an electric mixer until creamy.
Slowly pour in sugar, and then the egg, beating each until well combined.
Combine vanilla extract with milk in a measuring cup.
With mixer on LOW, alternately add in dry ingredients and milk/vanilla mixture, until fully combined. Increase speed and mix until smooth.
Using a large spoon, divide batter evenly into prepared cupcake pan, filling ¾ full.
Bake on 300 F. for 25 minutes, or until a toothpick inserted in center comes out clean.
Place on a wire cooling rack to cool completely.