Start by browning the butter. You'll take ½ cup of butter (one stick) and melt in a medium saucepan, and then continue to cook past the point of boiling. You will do this over medium heat, past the point of the butter foaming, until it turns a nice golden brown, and has a nutty smell. Make sure you are stirring and watching it, because it will turn from perfectly brown to burnt fairly quickly. Once finished browning, pour all of it into a bowl and allow to cool completely.
Preheat oven to 350 F. Line two baking sheets with parchment paper.
Measure out ⅓ cup of pumpkin and place on a paper plate. Using some paper towels, blot the pumpkin, removing liquid until the paper towel wipes clean. When done the pumpkin should measure more like ¼ cup (60g).
Place browned butter and sugars in the bowl of a stand mixer, fitted with a paddle attachment and mix together. Add pumpkin, egg yolk and vanilla and mix again.
In a separate bowl, whisk together flour, baking soda, salt, pumpkin pie spice and cinnamon. Add flour mixture to bowl and mix on low, being careful not to overmix. I usually like to stop mixing when I still have flour remnants around the bowl. Fold in chocolate chips, saving a handful to stick on top of the dough balls.
Scoop the dough into large balls, I like to use a ¼ cup cookie scoop. Roll the cookies slightly and push down just a bit so they aren't quite so tall. Top with a few extra chocolate chips and sprinkle with a bit of flaked salt if desired.
Bake the cookies for 9-11 minutes. You don't want to see any shiny dough in the middle of the cookie, but make sure not to over bake these. Allow cookies to cool on the pan before moving to a cooling rack to hold their shape.