Preheat the oven to 350°F (175°C) and grease or line a muffin tin with paper liners.
In a large mixing bowl, whisk together the flour, baking soda, baking powder, cinnamon, nutmeg, and salt until well combined.
In another bowl, mix the pumpkin puree, granulated sugar, brown sugar, vegetable oil, eggs, and vanilla extract until smooth.
Gradually add the wet ingredients to the dry ingredients, stirring gently until just combined. Avoid overmixing.
If desired, fold in chopped nuts or chocolate chips.
Divide the batter evenly among the 12 muffin cups, filling each about ⅔ full.
Bake in the preheated oven for 18 to 20 minutes, or until a toothpick inserted into the center comes out clean.
Allow the muffins to cool in the pan for 5 minutes before transferring them to a cooling rack.