01 -
Place peanut butter in a heat-safe bowl and microwave for 20 to 30 seconds until pourable but not hot. Line a metal 8-inch square pan with parchment paper, leaving an overhang. Spread the peanut butter in an even layer in the pan. Freeze for 1 hour or until solid. Lift peanut butter sheet from the pan using parchment, then return it to the freezer while you prepare the brownie mixture.
02 -
Preheat the oven to 350°F (175°C). Line the 8-inch square pan again with fresh parchment paper, leaving an overhang for easy removal.
03 -
In a large microwave-safe bowl, combine unsalted butter and chopped semisweet chocolate. Microwave in 30-second intervals, stirring after each, until fully melted and smooth.
04 -
Add granulated sugar to the hot butter-chocolate mixture and whisk vigorously until combined. Let the mixture cool until just barely warm.
05 -
Whisk in eggs, egg yolk, and vanilla extract for about 1 minute until well blended and slightly thickened.
06 -
Using a rubber spatula, stir in all-purpose flour, sifted unsweetened cocoa powder, and fine salt until just combined and no streaks remain.
07 -
Pour half of the brownie batter into the prepared pan and smooth the top. Carefully position the frozen peanut butter sheet over the batter. Gently spread the remaining brownie batter over the peanut butter layer, covering completely.
08 -
Bake in the preheated oven for approximately 30 minutes, until just set with a very slightly gooey center. Allow brownies to cool in the pan for 30 minutes, then remove and cool another 30 minutes before slicing and serving.