Preheat your oven to 350ºF (175ºC). Line an 8×8-inch metal baking pan with parchment paper.

In a large mixing bowl, whisk together the melted butter, brown sugar, and white sugar.

Melt the dark chocolate in a microwave-safe bowl, stirring every 20–30 seconds to avoid burning. Once melted, whisk it into the butter-sugar mixture.

Add the eggs one at a time, whisking well after each addition. Stir in the sourdough discard and vanilla extract until fully combined.

Add the cocoa powder, flour, and salt directly on top of the wet mixture. Use a spatula to fold everything together until the batter is smooth and thick.

Pour the brownie batter into the prepared pan and spread it evenly.

Drop 9 small spoonfuls of creamy peanut butter across the top. Use a knife to gently swirl the peanut butter through the batter.

Bake for 35–40 minutes, or until the edges and top are set. Avoid overbaking—check with a toothpick; it should come out with moist crumbs, not clean. For extra precision, the center should reach about 190ºF.

Let the brownies cool completely in the pan before slicing into squares.

Serve and enjoy!