Preheat the oven to 350°F (175°C). Line a 12-cup muffin tin with paper liners.
In a large bowl, whisk together flour, baking powder, baking soda, salt, cinnamon, and nutmeg.
In another bowl, combine mashed sweet potatoes, granulated sugar, brown sugar, melted butter, eggs, vanilla extract, and milk. Mix until well combined.
Gradually add the dry ingredients to the wet ingredients, mixing until just combined.
Divide the batter evenly among the prepared muffin cups.
Bake for 18-20 minutes, or until a toothpick inserted into the center of a muffin comes out clean.
Allow muffins to cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.
Notes
You can add chopped pecans or walnuts for extra texture and flavor.