Preheat the oven to 350F. Spray an 8x8-inch square baking pan with baking spray and line with parchment paper.

In a small saucepan, melt the butter over medium heat. Remove from the heat and whisk in ? cup chocolate chips until fully melted. Transfer to a large bowl and let cool for a few minutes.

In another bowl, sift together the flour and cocoa powder. Whisk in the salt.

To the melted chocolate, whisk in the sugars, eggs, and vanilla until smooth. Fold in the flour mixture until well combined. Fold in the remaining ? cup chocolate chips.

Pour the batter into the prepared pan and use a spatula to spread the batter to the edges of the pan.

Drop the peanut butter over the top of the batter by teaspoonfuls and swirl it into the batter with the tip of a knife or a skewer.

Bake for 40 to 45 minutes or until the center doesn?t wobble when the pan is gently shaken, or 35 minutes for a super fudgy center. Cover with foil after 25 minutes if the peanut butter appears to be browning.

Let the brownies cool in the pan completely before slicing.