01 - 
                Preheat oven to 350F. Spray an 8x8-inch square baking pan with baking spray and line with parchment paper.
              
              
              
                02 - 
                Melt butter in a small saucepan over medium heat. Remove from heat, whisk in 1/2 cup chocolate chips until fully melted. Transfer to a large bowl and let cool briefly.
              
              
              
                03 - 
                In a separate bowl, sift together flour and cocoa powder. Whisk in salt.
              
              
              
                04 - 
                Whisk sugars, eggs, and vanilla into the melted chocolate mixture until smooth. Fold in the flour mixture until just combined, then fold in remaining chocolate chips.
              
              
              
                05 - 
                Pour batter into prepared pan. Drop peanut butter by teaspoonfuls over the top and swirl gently with a knife or skewer.
              
              
              
                06 - 
                Bake for 40-45 minutes until center is set. Cover with foil after 25 minutes if peanut butter browns too quickly. Let cool completely before cutting.