Step 1: Preheat your oven to 350°F (175°C) and grease a 9x13 inch baking pan or line it with parchment paper for easy removal.
Step 2: In a medium bowl, whisk together the flour, pumpkin pie spice, baking soda, and salt until well combined.
Step 3: In a large bowl, cream together the softened butter, granulated sugar, and brown sugar until the mixture is light and fluffy.
Step 4: Beat in the egg and vanilla extract, followed by the pumpkin puree, mixing until smooth.
Step 5: Gradually add the dry ingredients to the wet ingredients, folding gently with a spatula just until the flour disappears.
Step 6: Spread the batter evenly into the prepared pan and bake for 25-30 minutes, or until a toothpick inserted in the center comes out clean.
Step 7: Allow the pumpkin bars to cool completely in the pan on a wire rack.
Step 8: Prepare the glaze by whisking together the powdered sugar, maple syrup, and melted butter until smooth. Drizzle or spread over the cooled bars and let set before slicing.