Preheat oven to 350°F. Line an 8x8 or 9x13 pan with parchment.
In a small saucepan, brown the butter by melting the butter over medium heat. Continue cooking until golden brown with a nutty aroma (3–5 minutes).
In a large bowl, whisk together ½ cup browned butter, ½ cup pumpkin purée, 1 ½ cup brown sugar, 2 eggs, and 2 tsp vanilla until smooth.
In a separate bowl, whisk 2 ⅔ cup flour, 1 tbsp pumpkin pie spice, 1 tsp baking powder, 1 tsp baking soda, and 1 tsp salt.
Stir dry ingredients into the wet ingredients until just combined.
Spread batter evenly in the prepared pan. (If using an 8x8 pan, it will result in a thicker blondie which will take longer to bake- about 30-38 minutes. If using a 9x13 pan, it will be thinner and will take less time- 20–28 min)
Test doneness with a toothpick — it should come out with a few moist crumbs but not wet batter.
Cool completely before cutting into bars.