Preheat oven to 350 degrees F.

Line an 9x13 baking dish with parchment paper or aluminum foil allowing excess foil to hang over pan edges, and lightly grease with cooking spray. Set aside

Combine flour, baking powder, and salt in a small bowl; set aside.

In a mixing bowl with electric mixer, beat melted butter, brown sugar and peanut butter until smooth and creamy.

Beat in the egg and vanilla. Slowly add dry ingredients and stir until just incorporated.

Add the peanuts and mix until evenly distributed.

Spread the batter mix into the prepared baking dish and spread out evenly with a plastic spatula.

Bake for 25-305 minutes or until a tooth pick inserted in the middle comes out clean or with a few moist crumbs attached.

Cool completely on a wire rack for at least 2 hours.

Using the foil overhang, lift the blondies from the pan and transfer to a cutting board.

Cut into 2 inch squares and serve.

Store in an airtight container at room temperature, or airtight container in the refrigerator for one week.