In a heavy bottom sauce pan heat your butter carefully until it is browned stirring continuously. Simmer until the butter is giving off a nutty scent and has browned.Once browned take it off the heat and let it come to room temperature for an hour or so.
Over a small bowl place the pumpkin puree in several layers of cheesecloth or paper towels and press gently to remove the extra liquid until 1 cup of pumpkin puree gets reduced to ⅓ cup.
Preheat the oven to 350/170 degrees. Spray a 8*8 inch square pan with non stick spray and line it with parchment paper.
In a medium mixing bowl whisk together all purpose flour, pumpkin pie spice, baking soda, and salt. Set aside.
In the bowl of an electric stand mixer fitted with the paddle attachment or in a bowl with a hand mixer, beat together the browned butter and dark brown sugar for 2-3 minutes until well combined.
Beat in egg and vanilla until well combined, then on low speed blend in the pumpkin puree.
Add the flour mixture and gently stir just until no specs of flour remain. Fold in the white chocolate chips.
Spread batter evenly into the prepared pan and level using an offset spatula Sprinkle the top evenly with a few white chocolate chips and cinnamon sugar.
Bake in preheated oven until bars are set (a toothpick should come out clean or with a moist crumb), about 25 - 30 minutes.
Cool completely then lift bars from pan using parchment, cut into squares.