In a medium bowl, combine all-purpose flour, cocoa powder, and salt until well incorporated. Set aside.

In a large bowl, whisk melted butter, melted chocolate, and granulated sugar until well incorporated. Whisk in eggs and vanilla extract until combined.

Add the dry ingredients to the wet ingredients. Using a spatula, combine the brownies batter until well combined. Do not overmix.

Pour the brownies batter to the prepared pan.

In a small bowl, mix peanut butter, melted butter, confectioners sugar, and vanilla extract until well combined.

Drop dollops of peanut butter on top of brownies batter. Using a toothpick or knife, swirl the peanut butter in an up and down motion. Then, repeat the same motion crosswise until the desired swirling is achieved.

Bake for 30 minutes or until a toothpick inserted in the center comes out with a couple of moist crumbs. Cool completely in the pan before slicing.