Preheat the oven to 350°F (175°C). Prepare a 13x9 inch baking pan by lining it with parchment paper or lightly spraying it with baking spray for easy removal.

Cream together the softened unsalted butter, granulated sugar, and brown sugar in a mixing bowl until creamy and well combined, about 2-3 minutes.

Incorporate the pumpkin puree, egg yolk, and vanilla extract into the butter mixture and beat until fully blended.

Combine the dry ingredients in a separate bowl: whisk together the all-purpose flour, pumpkin pie spice, salt, and baking powder.

Gradually mix the dry ingredients into the wet ingredients using low speed until just combined.

Spread the batter evenly into the prepared baking pan, smoothing the top with a spatula.

Prepare the topping by mixing together the granulated sugar and ground cinnamon. Sprinkle over the batter.

Bake in the preheated oven for about 25 minutes, or until a toothpick inserted into the center comes out clean.

Cool the blondies in the pan before cutting into squares.