Preheat oven to 350 degrees. Line 8-10 standard muffin cups with paper liners or spray generously with non-stick cooking spray.
In a large bowl beat together the butter and sugar until smooth. Add the egg and continue to beat until blended.
In a separate bowl whisk together the flour, baking soda, baking powder, salt, nutmeg and cinnamon.
Combine buttermilk and vanilla in a measuring cup.
Add half the flour mixture to the butter mixture, then add half the buttermilk mixture. Stir. Repeat with next half of each and stir until just moistened. Do not over mix.
Use a large ice cream scoop and scoop batter into cups until 3/4 full. Bake for 20-22 minutes or until toothpick inserted in center of muffin comes out clean.
Let the muffins cool in the pan for 5 minutes, then place on a wire rack.
For the topping:
Combine the granulated sugar and cinnamon in small bowl.
Melt the butter in another bowl.
Dip the top of the muffin into the melted butter coating the entire top evenly, then into the cinnamon sugar mixture. Place on wire rack.
These muffins freeze really well too. Place extras in a Ziploc freezer bag and when you want one pop it out of the freezer and let it defrost on a plate on the counter. Then I place mine in the microwave for 10-15 seconds and it is warm and delicious with my coffee.