Preheat the oven to 350F. Line a cookie sheet with parchment paper.
Start by melting the butter on the stove-top. Slice the butter then add it to a medium pot over medium heat. Once melted, remove from heat.
Roughly chop the baking chocolate into a variety of sizes. Small pieces of chocolate will create swirls of melted chocolate, while larger chunks will make chocolate puddles. Set aside.
For cookies with melted chocolate throughout, use the pot with the melted butter to make the cookie dough. For cookies with less melted chocolate, transfer the melted butter to a new mixing bowl.
To the melted butter add the brown sugar, granulated sugar, and pumpkin puree. Stir until well combined. Whisk in the egg yolk, stirring continuously until evenly distributed.
In a separate bowl, whisk together the all-purpose flour, baking soda, salt, cinnamon, and pumpkin pie spice. Add half of this to the wet ingredients, stirring until well combined. Stir in the remaining flour mixture.
Fold in the chocolate chips and chopped chocolate. The more the dough is stirred, the more the chocolate will melt and distribute throughout the dough.
Use a 1-ounce (2 tablespoons) cookie scoop to portion cookie dough on a parchment paper-lined baking sheet. Leave 3 inches between cookie dough.
Bake at 350F for 9-11 minutes, or until the edges of the cookies are set. Remove from the oven and sprinkle with optional flakey salt. Transfer to a wire cooling rack once firm enough to handle. Enjoy!
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Notes
Chocolate: I use unsweetened baking chocolate, but I realize not everyone likes very bitter chocolate, so the recipe is written for semi-sweet chocolate (56% cacao.) Most of the chocolate swirls come from the little pieces of shaved chocolate created while chopping the baking chocolate.
This recipe works with 100% chocolate chips if you don't have baking chocolate on hand, just note that the cookies won't have as many chocolate swirls.