Preheat oven to 350°F (175°C) and grease a standard 9x5 inch loaf pan.
In a large mixing bowl, cream together the softened butter and 1 cup of sugar until light and aerated.
Add the egg and vanilla extract to the butter mixture and beat until fully incorporated.
In a separate medium bowl, sift together the flour, baking powder, baking soda, salt, and nutmeg.
Add the dry ingredients to the wet mixture in three parts, alternating with the buttermilk, starting and ending with the dry ingredients. Stir only until combined.
Transfer the batter to the prepared loaf pan and smooth the top with a spatula.
Bake for 45 to 50 minutes, or until a toothpick inserted into the center of the loaf comes out clean.
Allow the bread to cool in the pan for 10 minutes before transferring it to a wire rack.
In a shallow dish, whisk together the topping sugar and cinnamon.
While the bread is still warm, brush the entire exterior with melted butter and roll in the cinnamon-sugar mixture until evenly coated.