Preheat oven to 350 degrees F.

Line a 9×9-inch square pan with two sheets of parchment paper, trimmed and placed one across left to right, then top to bottom, making sure that the edges of the paper are large enough to extend up the sides of the pan. (This will make it easier to lift the baked blondies out of the pan to cut.) Set pan aside.

In a small bowl, whisk together flour and baking powder to combine. Set aside.

In the bowl of a mixer, combine melted butter, peanut butter, and both sugars. Mix well, scraping the sides and bottom of the bowl as needed.

Add eggs to the mixing bowl, one at a time, mixing well after each addition. Add vanilla extract and salt and mix one more time to combine. At this point, you are done with the mixer.

One third at a time, slowly fold the flour mixture into the peanut butter mixture, stirring just enough to incorporate the flour after each addition. When you add the last third of the flour mixture, also add the chocolate chips and gently stir just until combined and the chips are evenly dispersed throughout the batter.

Spoon the batter into the prepared pan, spreading evenly to the corners. Bake for 20-25 minutes, until the edges are lightly golden brown and the inside is just set. (The middle will still be soft to the touch – it will firm up a bit as it cools.)

Place pan on a cooling rack and allow the blondies to firm up for about 10 minutes. Use the parchment paper handles to carefully lift the blondies back onto the cooling rack. Once completely cool, cut into 9 large (3 rows x 3 rows) or 16 smaller pieces (4 rows x 4 rows).