In a heat-safe bowl, microwave the peanut butter for 20 to 30 seconds until it becomes pourable but not too hot.

Line an 8-inch square metal pan with parchment paper, ensuring there's an overhang.

Spread the warmed peanut butter evenly in the pan and freeze for 1 hour or until it solidifies.

Once solid, use the parchment to lift the peanut butter sheet out of the pan and return it to the freezer while you prepare the brownie batter.

Preheat your oven to 350°F and line the square pan again with parchment paper, leaving an overhang.

In a large microwave-safe bowl, combine the butter and chopped chocolate.

Microwave the mixture in 30-second intervals, stirring in between, until it is melted and smooth.

Stir in the granulated sugar into the warm butter and chocolate mixture, whisking until well combined.

Allow the mixture to cool until it is just warm, then add the eggs, egg yolk, and vanilla extract, whisking for about 1 minute until fully incorporated.

Using a rubber spatula, gently fold in the flour, cocoa powder, and fine sea salt until just combined.

Pour half of the brownie batter into the prepared pan and smooth it out evenly.

Carefully place the frozen peanut butter sheet on top of the batter.

Pour the remaining brownie batter over the peanut butter, ensuring it is completely covered.

Bake in the preheated oven for about 30 minutes, or until the brownies are cooked through but still slightly gooey in the center.

Let the brownies cool in the pan for 30 minutes.

Remove the brownies from the pan and allow them to cool for another 30 minutes before slicing and serving.

These brownies can be stored in an airtight container at room temperature for up to 3 days or in the fridge for up to 5 days. Chilling them makes them extra fudgy!