Preheat oven to 350°F (175°C). Grease or line a 12-cup muffin tin.
Whisk together flour, sugar, baking powder, salt, and nutmeg.
In another bowl, whisk milk, egg, butter, and vanilla.
Mix wet into dry ingredients just until combined.
Divide batter into muffin cups, filling ⅔ full.
Bake 20–25 mins until a toothpick comes out clean.
While baking, mix cinnamon sugar and melt butter in two bowls.
Dip warm muffins in melted butter, then coat with cinnamon sugar.
Serve warm or cool — either way, they’re irresistible!