Preheat your oven to 375°F (190°C) and lightly grease a 12-cup muffin pan with melted butter
In a large bowl, cream together the softened butter and sugar until light and fluffy.
Beat in the eggs one at a time, scraping down the sides of the bowl after each addition. Stir in the vanilla extract.
In a separate bowl, combine the baking powder, baking soda, salt, and flour.
Add the dry ingredients to the butter mixture in two additions, alternating with the milk. Start and end with the dry ingredients. Stir just until combined; do not over mix.
Spoon the batter evenly into the prepared muffin cups, filling each about 2/3 full.
Bake the muffins for 18-20 minutes, or until they're a pale golden brown and a toothpick inserted into the middle of one of the center muffins comes out clean.
While the muffins are baking, prepare the cinnamon sugar coating. In a small bowl, mix together the sugar and cinnamon. Melt the butter in a separate bowl.
Once the muffins are done, let them cool in the pan for about 5 minutes. After they have cooled slightly, remove them from the pan. Dip each muffin top in the melted butter, then roll in the cinnamon sugar to coat.
Place the coated muffins on a wire rack to cool completely. Serve and enjoy!