1. Preheat your oven to 350°F (175°C) and prepare an 8×8 or 9×13 inch baking pan by lining it with parchment paper or lightly greasing it.
2. In a medium bowl, whisk together melted butter and sugars until smooth and creamy.
3. Add pumpkin puree and vanilla extract to the butter-sugar mixture and mix until fully incorporated.
4. Beat in the eggs or egg yolks one at a time, making sure each is well mixed before adding the next.
5. In a separate large bowl, sift together all-purpose flour, baking soda, baking powder, salt, pumpkin pie spice, and cinnamon.
6. Gradually add the dry ingredients to the wet mixture, stirring gently with a spatula or wooden spoon, being careful not to overmix.
7. In a small bowl, prepare the cinnamon sugar topping by mixing a few tablespoons of granulated sugar with ground cinnamon.
8. Pour the prepared batter into the baking pan and spread it evenly with a spatula.
9. Sprinkle the cinnamon sugar mixture generously over the surface of the batter.
10. Bake the bars in the preheated oven for 35-38 minutes, checking for doneness with a toothpick (it should come out mostly clean with a few moist crumbs).
11. Allow the bars to cool in the pan for about 15 minutes on a wire rack.
12. Once cooled, transfer the bars to a cutting board and slice them into your desired size.
13. Serve the bars as they are or enhance them with a scoop of vanilla ice cream, cream cheese frosting, or a drizzle of caramel sauce for added flavor.
14. Enjoy your Pumpkin Snickerdoodle Bars as a fall-inspired treat!