Preheat oven to 350°F (175°C).
Grease a 12-cup muffin tin or line with paper liners.
In a bowl, whisk together flour, baking powder, salt, and nutmeg.
In a separate bowl, whisk sugar, melted butter, egg, milk, and vanilla until smooth.
Gradually add the dry ingredients to the wet ingredients and stir just until combined.
Fill muffin cups about ¾ full.
Bake for 15–18 minutes, or until a toothpick inserted in the center comes out clean.
Let cool for 5 minutes in the pan.
Mix the sugar and cinnamon in a shallow bowl.
Brush each warm muffin with melted butter.
Roll or sprinkle generously with the cinnamon-sugar mixture until fully coated.
Enjoy warm with coffee, tea, or a glass of milk!
