01 - Preheat oven to 350°F. Line an 8x8-inch baking pan with parchment paper, leaving overhang for easy removal.
02 - Whisk melted butter and sugar in a large bowl until smooth. Add eggs and vanilla, whisking until well combined. Sift in cocoa powder, flour, and salt. Mix until just combined.
03 - Spread batter evenly in prepared pan. Bake for 22-25 minutes until a toothpick inserted in center comes out with moist crumbs. Cool completely in pan.
04 - Beat peanut butter, melted butter, powdered sugar, vanilla, and salt in a medium bowl until smooth and creamy. Spread evenly over cooled brownie base.
05 - Refrigerate for 30 minutes to set the peanut butter layer.
06 - Place chocolate chips in a heatproof bowl. Heat heavy cream until simmering, then pour over chocolate. Let sit 2 minutes, then stir until smooth.
07 - Let ganache cool slightly, then pour and spread over peanut butter layer. Refrigerate at least 1 hour until set. Lift from pan using parchment, cut into squares.