Microwave 1 cup of creamy conventional peanut butter in short bursts until pourable, about 20-30 seconds. Line an 8-inch square pan with parchment paper and spread the melted peanut butter in an even layer. Freeze for at least 1 hour.

Preheat your oven to 350°F (175°C). Reseal the lined pan with parchment paper.

Combine 1/2 cup unsalted butter and 4 oz. semisweet baking chocolate in a microwave-safe bowl. Heat in 30-second intervals until smooth, then stir in 1 cup granulated sugar until well combined.

After cooling slightly, whisk in 2 large eggs, 1 egg yolk, and 1 tsp vanilla extract. Gently fold in 1 cup all-purpose flour, 1/3 cup cocoa powder, and 1/4 tsp fine sea salt until just combined.

Pour half of the brownie batter into the prepared pan. Place the frozen peanut butter layer on top, then cover with the remaining brownie batter.

Bake for approximately 30 minutes. They’re ready when a toothpick inserted comes out with a few moist crumbs.

Let the brownies cool in the pan for 30 minutes, then lift them out using the parchment. Cool for another 30 minutes before cutting into squares.