Heat griddle to 375°F.
Whisk together flour, baking powder, baking soda, salt, sugar, cinnamon and nutmeg in a medium bowl.
Add egg, buttermilk, and 2 tablespoons butter using a whisk until just combined. Stir in the mashed sweet potato. Do not over mix; the batter should have small lumps.
Test griddle by sprinkling a few drops of water on it. If water bounces and splatters off griddle, it is hot enough. Using a pastry brush, brush remaining ½ teaspoon of butter onto griddle. Wipe off excess with a paper towel.
Using an ice cream scoop or ladle, pour pancake batter (about half a cup), 2 inches away from one another. When pancakes have bubbles on top and are slightly dry around edges, about 2½