Preheat your oven to 375°F (190°C) and lightly grease a 12-cup muffin tin.
In a small bowl, combine flour, pumpkin pie spice, cinnamon, baking powder, and sea salt. Set aside.
In a large bowl, whisk together pumpkin puree and melted butter until smooth.
Add brown sugar and granulated sugar, whisking until fully dissolved.
Mix in eggs and vanilla extract until evenly incorporated.
Gradually fold in the dry ingredients until the batter is smooth. Avoid overmixing.
If desired, stir in optional mix-ins such as chocolate chips or nuts.
Divide the batter evenly into the muffin tin, about ¼ cup per cup, and smooth the tops.
Bake for 20–25 minutes, or until a toothpick inserted in the center comes out clean or with a few crumbs. For high-altitude baking, reduce to 15–18 minutes.
Allow muffins to cool in the tin for 10 minutes, then transfer to a wire rack to cool completely.
