Preheat the oven to 375°F (190°C). Line a muffin pan with paper liners or lightly grease each cup.
Whisk together the flour, baking powder, baking soda, pumpkin pie spice, cinnamon, nutmeg, and salt until evenly combined.
In a separate bowl, whisk the pumpkin puree, granulated sugar, brown sugar, vegetable oil, eggs, vanilla extract, and milk until smooth.
Add the dry ingredients to the wet mixture and gently fold everything together just until no dry streaks remain. Avoid overmixing.
Divide the batter evenly among the prepared muffin cups, filling each about three-quarters full. Sprinkle the tops with coarse sugar and a pinch of pumpkin pie spice if using.
Bake until the muffins are beautifully risen and a toothpick inserted into the center comes out clean.
Allow the muffins to cool in the pan for a few minutes before transferring them to a wire rack to cool completely.