Preheat the oven to 375°F (190°C). Line a 12-cup muffin tin with liners or grease lightly.
In a large bowl, whisk together the flour, granulated sugar, brown sugar, baking soda, baking powder, salt, and spices until well combined and no sugar lumps remain.
In a separate bowl or large measuring cup, whisk the pumpkin puree, eggs, oil, milk, and vanilla until smooth.
Pour the wet ingredients into the dry.
Stir gently with a spatula until just combined. Do not overmix; a few small streaks of flour are fine.
Fold in any optional mix-ins like chocolate chips or nuts.
Divide the batter evenly among the muffin cups, filling each about 3/4 full. Sprinkle tops with coarse sugar if using.
Bake for 18–22 minutes, or until a toothpick inserted in the center comes out clean or with a few moist crumbs.
Cool in the pan for 5 minutes, then transfer to a wire rack to cool completely. Enjoy warm or at room temperature.