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