Preheat your oven to 350°F (175°C) and prepare a 9x13 inch baking pan.

In a medium bowl, whisk together 1 ½ cups of all-purpose flour, 1 teaspoon of baking powder, and 1 tablespoon of pumpkin pie spice.

In a large mixing bowl, combine ½ cup of melted unsalted butter, ½ cup of granulated sugar, and ½ cup of brown sugar until smooth. Add in 1 egg, 1 cup of pumpkin puree, 1 teaspoon of vanilla extract, and a pinch of kosher salt, mixing well.

Gradually add the dry mixture from Step 2 into the bowl with the wet ingredients and stir until just combined.

Spread ⅓ to ½ of the prepared batter at the bottom of your baking pan, sprinkle chocolate chips and dollops of marshmallow fluff, then pour remaining batter to cover.

Bake in the preheated oven for 30 to 50 minutes. Check with a toothpick for doneness.

Cool completely before slicing into squares for serving.