Preheat the oven to 325°F. Line an 8x8-inch baking pan with parchment paper.
In the bowl of a stand mixer fitted with the paddle attachment, add the butter, dark brown sugar, and vanilla extract. Mix on low until combined and there are no chunks of butter.
Add the pumpkin puree, then the dry ingredients: flour, pumpkin spice, baking soda, and sea salt. Mix on low until a stiff cookie dough forms.
Place three-quarters of the dough (just eyeball it) into the baking pan and press it with your hands to form an even layer.
Top the cookie dough with the marshmallow crème and spread evenly for the marshmallow layer.
Break the graham crackers into pieces and sprinkle the chocolate chips and graham crackers on top of the marshmallow.
Add the remaining cookie dough on top by breaking it into little chunks and adding evenly on top of the bars, allowing parts of marshmallow crème, chocolate chips, and graham crackers to show through.
Bake for 30 to 35 minutes or until the cookie portion looks lightly browned and it’s only a little jiggly. Allow to cool completely in the pan.
Cut the bars into 9 bars. Store in an airtight container for up to 5 days.