Preheat the oven to 350F with the top rack in the middle position. Line a 12-muffin pan with liners. You can also grease it.
Make the muffin batter:
In a large bowl, combine the flour, sugar, baking powder, baking soda, cinnamon, pumpkin spice, and salt. Mix well with a whisk to distribute the ingredients.
In a medium bowl, whisk the eggs. Then, add the pumpkin pureé, milk, and melted (and cooled) butter (or a neutral oil). Pour the liquid mixture into the bowl with the dry ingredients, and gently mix until combined. The batter is thick. Add the chocolate chips to the bowl and gently fold them in.
Scoop the batter into the muffin cups, filling each nearly to the top. I like to lift the batter from the bottom of the bowl to catch the chocolate chips that sink.
Bake:
Bake the muffins for 20 to 22 minutes, until the tops are golden and a toothpick comes out clean when inserted in the middle. Remove the muffin pan from the oven and let the muffins cool completely before taking them out.
Store:
Muffins can be stored in an airtight container at room temperature (on the counter) for 1 day, in the refrigerator for up to 5 days, or in the freezer for up to 3 months.