Preheat oven to 350°F (175°C). Line a muffin tin with paper liners or lightly grease.
In a large bowl, cream together the butter and sugar until light and fluffy.
Beat in the egg and vanilla extract until well combined.
In a separate bowl, whisk together the flour, baking powder, baking soda, salt, cinnamon, and nutmeg.
Gradually add the dry ingredients to the wet ingredients, alternating with buttermilk, starting and ending with the dry ingredients.
Mix until just combined; do not overmix.
Spoon the batter evenly into the prepared muffin tin, filling each about 2/3 full.
Bake for 18-20 minutes, or until a toothpick inserted into the center comes out clean.
Let muffins cool for 5 minutes before removing from the tin.
While muffins are still warm, dip the tops in melted butter and roll generously in cinnamon sugar.