Preheat your oven to 375°F (190°C). Grease a muffin tin or line it with paper liners.
In a mixing bowl, whisk together the flour, baking powder, ground cinnamon, salt, and granulated sugar.
In another bowl, whisk together the melted butter, vanilla extract, egg, and milk until smooth.
Gradually add the wet ingredients to the dry ingredients, stirring gently until just combined. Do not overmix.
Fill each muffin cup about 2/3 full with the batter. Bake for 18-20 minutes, or until a toothpick inserted into the center comes out clean.
Let the muffins cool for 5 minutes in the pan, then transfer to a cooling rack.
For the coating, mix the granulated sugar and ground cinnamon in a small bowl. Dip the top of each muffin in melted butter, then coat with the cinnamon-sugar mixture.
Serve warm or at room temperature. Enjoy!
Notes
These muffins can be stored in an airtight container for up to 3 days. Reheat in the microwave for a few seconds to enjoy them warm!