Preheat your oven to 350°F (175°C) and line a cupcake pan with paper liners.
In a medium bowl, whisk together the flour, baking powder, baking soda, salt, and ground cinnamon. Set aside.
In a large mixing bowl, cream the softened butter and sugar together until light and fluffy, about 3-4 minutes.
Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.
Gradually add the dry ingredients to the wet mixture, alternating with the buttermilk, starting and ending with the dry ingredients. Mix until just combined.
Divide the batter evenly among the cupcake liners, filling each about two-thirds full.
Bake for 18-20 minutes, or until a toothpick inserted into the center comes out clean. Allow the cupcakes to cool in the pan for 5 minutes before transferring them to a wire rack to cool completely.
For the cinnamon sugar topping, combine the sugar and cinnamon in a small bowl. Dip the tops of the cooled cupcakes into the melted butter, then into the cinnamon sugar mixture to coat.
Serve immediately or store in an airtight container for up to 3 days.