Preheat the oven to 350°F (175°C). Line a 12-cup muffin pan with paper liners or grease well.

In a large bowl, whisk together the flour, granulated sugar, brown sugar, baking soda, baking powder, pumpkin pie spice, cinnamon, and salt.

In a separate bowl, whisk together the pumpkin puree, vegetable oil, eggs, milk, and vanilla extract until smooth.

Add the wet ingredients to the dry ingredients and stir gently until just combined. Do not overmix.

Fold in the chopped pecans or walnuts if using.

Divide the batter evenly among the muffin cups, filling each about 3/4 full.

Top each muffin with a few pepitas and extra chopped nuts if desired.

Bake for 18 to 22 minutes, or until a toothpick inserted into the center comes out clean or with a few moist crumbs.

Let the muffins cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.