In a light-colored skillet, heat the butter over medium heat until melted, whisking occasionally. The butter will begin to sizzle and make crackling sounds as the moisture cooks off and the milk solids separate and settle to the bottom of the pan. Continue cooking, whisking frequently, until the milk solids turn golden brown and the butter smells nutty.
When the butter has browned immediately remove from the heat and transfer to the mixing bowl you will be using. Make sure to scrap all of the browned bits into the bowl (that's where you get all that amazing flavor!)
Whisk in the espresso powder, cinnamon and pumpkin pie spice. Set aside to cool for about 20 minutes.
While butter is cooling add the pumpkin to a plate lined with paper towels. Blot the moisture away from the pumpkin. You want it to be the consistency of dough and about ⅓ cup after removing the water.
Preheat oven to 350℉. Line a cookie sheet with parchment paper.
Once the butter has cooled whisk in both types of sugar, the egg, vanilla extract and blotted pumpkin puree.
In a separate bowl mix together the flour, baking soda and salt.
Mix the flour mixture into the pumpkin mixture. The dough will be thick but will come together mixing with a spatula. Mix until there are no white streaks of flour remaining. Add the chocolate chips and ¾ of the chopped chocolate bar. Reserve the rest to add to the top after it comes out of the oven.
Use a #20 cookie scoop (about 3 tablespoons) to scoop the dough onto the parchment lined tray about 3 inches apart. Bake in preheated oven for 12 minutes. Half way thru quickly open the oven and take the tray and slightly bang it on the rack a few times. This pan banging method encourages the cookies to spread a little more and creates a little rippled edge that is amazingly crispy!
After the 12 minutes remove the rack from the oven and let the cookies cool on the cookie sheet. Add a few bits of chocolate to the top to get those melty chocolate pools on the top. Sprinkle with flaky sea salt if desired.
Once cool the cookies will stay fresh in a airtight container at room temperature for 3-4 days.