Preheat your oven to 375°F (190°C). Grease or line a muffin tin.
In a large bowl, whisk together the gluten-free flour, baking powder, baking soda, salt, cinnamon, and nutmeg.
In another bowl, mix the mashed sweet potatoes, brown sugar, milk, vegetable oil, eggs, and vanilla extract until well combined.
Pour the wet ingredients into the dry ingredients and stir until just combined. Do not overmix.
Divide the batter evenly among the muffin cups.
Bake for 20-25 minutes, or until a toothpick inserted into the center comes out clean.
Allow the muffins to cool in the tin for 5 minutes, then transfer to a wire rack to cool completely.