Preheat your oven to 350°F (175°C) and grease a 9.25 x 5.25 inch loaf pan.
In a large mixing bowl, cream together the softened butter and sugar until light and fluffy.
Add the eggs one at a time, then mix in the vanilla extract followed by the mashed sweet potatoes.
In another bowl, whisk together the flour, baking soda, salt, ground cinnamon, and ground nutmeg.
Gradually add the dry ingredients to the wet mixture until just combined, then pour the batter into the prepared loaf pan.
In a small bowl, mix together the topping sugar and cinnamon before sprinkling it over the top of your batter.
Bake for about 55–65 minutes, checking for doneness with a toothpick.