I have lots of notes/trouble-shooting/reasons behind the method throughout this post. The detailed instructions are to help you get the exact texture shown in the pictures and described in the post.
In a large bowl, with hand mixers beat together the butter (softened and not melted) with the brown sugar and white sugar.
Beat in the pumpkin, egg yolk, and vanilla. (Make sure your canned pumpkin is high quality and not watery. If it is watery your cookies will be more cakey. Drab the pumpkin with some paper towels if needed.)
In another bowl stir together the flour, quick oats, cinnamon, pumpkin pie spice, baking soda, baking powder, and salt. If you like more seasonings in your pumpkin cookies (we just like cinnamon) feel free to add them here. Some ideas would be some pumpkin pie spice, more cinnamon, a little bit of nutmeg, allspice, cloves, etc.
Please note as you measure your flour that packing in too much flour will also lead to cakey cookies. I spoon the flour into the measuring cup and then level it at the top with my finger without pressing it down. Too little flour and your cookies will spread way too much and too much flour and they will be cakey. If experiencing either of these problems, you likely measured your flour incorrectly.
Add the dry to the wet and mix until just combined.
The mixture should pull away from the edges once all the flour is added. Stir in the chocolate chips (I use and prefer regular sized milk chocolate chips with the miniature semi-sweet mixed together, but use what you like!).
Cover and place in the fridge for at least 30 minutes and preferably 1 hour. This is a crucial step and if skipped your cookies will likely spread like a pancake.
Preheat the oven to 350 degrees F.
Once the dough has been chilled, line a baking mat with a nonstick liner (or parchment paper). (The times I haven't used the liners the bottom of these cookies cook faster than the tops are cooked and have the tendency to slightly burn at the edges)
Roll two small balls of dough and the press one ball on top of the other and mesh together into one tall piece without flattening. This forms a tallish, almost vertical rectangle shape - this is how I get the cookies to look like they do and have that crisp exterior + chewy interior. Basically the bottom of the tall rectangle cookie cooks first and then the top section cooks next but for slightly less time. So that is why this shape is so important to getting your cookie to look like the ones I have pictured and have the texture described).
Once you've rolled about 6-8 balls of dough, chill on the cookie sheet in the fridge for another 10-15 minutes. (I only put 6-8 cookies on a cookie sheet as they spread quite large depending on how much dough you have rolled -- I use 3-4 tablespoons per cookie)
While one batch is chilling you can work on rolling out another one.
Take the tray right from the fridge and place it in the oven.
Bake for 12-14 minutes or until very lightly browned at the bottom/sides. The key to these cookies is slightly under-baking - that will keep them soft and chewy in the inside.
Remove from the oven and allow to "cook" for another 1-2 minutes on the baking sheet before removing them to a wire cooling rack. This is optional but huge for appearance: I press in 5-6 additional chocolate chips into the tops of each of the cookies as soon as I remove them from the oven.
These cookies taste even better the next day -- the cinnamon and pumpkin flavor have definitely intensified by then!
Store in an airtight container.