Preheat oven to 325℉
In a small bowl, whisk together flour, baking powder, cinnamon, and salt. Set aside.
In your main mixing bowl, cream together softened butter and sugar. Mix on medium for 2-3 minutes. The mixture should have become whiter in color by now.
Stir in the eggs. Mix for another 2 minutes on medium speed.
Add sour cream and vanilla. Mix until incorporated.
While mixing on a low speed, add in the dry ingredients. Add the milk right after. Mix until combined and do not over mix. It is best to only mix your batter for 1 minute once all the ingredients are added.
Scoop into lined cupcake pans and bake!
Bake for 27-30 minutes. Check on them after 25 minutes. All ovens tend to be a bit different.
Once a toothpick inserted comes out clean or with very few moist crumbs, you are ready to take the cupcakes out of the oven.
Cool on a wire rack while you make the icing.