Preheat your oven to 350°F (175°C) and line a muffin tin with cupcake liners.
In a bowl, whisk together the flour, baking powder, salt, and cinnamon.
In another bowl, beat the butter and sugar until light and fluffy. Add the eggs one at a time, then mix in the vanilla extract.
Gradually add the dry ingredients to the wet ingredients, alternating with the milk. Mix until just combined.
Divide the batter evenly among the cupcake liners. Bake for 18-20 minutes or until a toothpick inserted into the center comes out clean.
While the cupcakes are baking, mix the sugar and cinnamon for the topping in a small bowl.
Once the cupcakes are done, let them cool for a few minutes. Brush the tops with melted butter and dip them into the cinnamon sugar mixture.