Preheat the oven to 350°F. Prepare a 9 × 9-inch baking pan with cooking spray and 2 sheets of parchment.

In a medium mixing bowl, add the creamy peanut butter and confectioners sugar. Beat with a hand-mixer until well-combined and smooth. Set aside.

Add the chopped chocolate to a heatproof bowl and place over of a pot of simmering water, ensuring the bowl fits tightly over the pot of water and that the bottom of the bowl does not touch the water. Heat, while stirring with a rubber spatula, until all the chocolate has melted. Set aside to cool slightly while you make the rest of the batter.

In a large mixing bowl, add the white sugar, brown sugar and eggs. Whisk together by hand for about 1 minute. The mixture should look creamy and well combined. Next, pour in the butter, vanilla and melted chocolate. Whisk together until well combined.

In a separate bowl, whisk together the flour, sifted cocoa powder and salt. Sift these dry ingredients into the wet ingredients, then fold the sifted dry ingredients into the batter with a rubber spatula, until the batter is smooth, well combined and thick.

Pour the half of the batter into the prepared pan. Evenly spread the peanut butter/confectioners sugar mixture over top. Finally, top with the remaining brownie batter and ensure that you evenly spread the batter over top of the peanut butter layer.

Dollop the natural peanut butter (if using) across the top of the brownies, then swirl it around using a wooden skewer. Place into the oven to bake for 40 to 50 minutes. When done, the brownies will seem slightly jiggly in the centre, but they will continue to set as they cool.

Allow the brownies to cool completely in the pan. When ready to serve, use a hot or wet knife to slice the brownies for easier and smoother cutting.