Preheat oven to 350F and cover 2 baking sheets with parchment paper.
Combine dry ingredients (all-purpose flour, rolled oats, baking soda, salt, cinnamon) in a medium sized bowl.
In a large bowl, use a wooden spoon to cream the butter and both sugars until smooth. You may use a stand mixer if you prefer. Add egg and vanilla and stir.
Alternately add pumpkin purée and dry ingredients to sugar mixture until well combined, beginning and ending with the dry ingredients.
Stir in the chocolate chips.
Drop by heaping tablespoonfuls on a baking sheet covered in parchment paper. Bake for 20-22 minutes until lightly browned underneath.
Transfer to a wire rack to cool before serving.
Notes
Remove the butter from the refrigerator about 2 hours ahead to ensure that it is at room temperature.
Be sure to purchase canned pumpkin purée that is not already spiced. Or use your own homemade purée!
If you prefer a higher cookie dough to chocolate chip ratio, increase the amount of chocolate chips to 1 cup.
You don't need to flatten the dough once you place it on the baking sheet. The cookies will spread slightly as they bake. Be sure to leave about 2 inches between each cookie.
They are done when lightly browned underneath.
Keep in a well sealed container at room temperature for up to 3 days.
Freeze the cookies in an airtight container for up to 3 months.