Preheat your oven to 350°F (175°C). Grease an 8×8 inch baking pan thoroughly.

Whisk together the dry ingredients: cocoa powder, flour, and granulated sugar.

Melt the butter gently over low heat and let it cool slightly before adding it to the mixture.

Add the eggs and vanilla extract, stirring gently until just combined.

Cream the peanut butter in a separate bowl, optionally adding powdered sugar for sweetness.

Layer the brownie batter in the pan, adding dollops of peanut butter and swirling gently.

Bake for 25-30 minutes until set but soft in the center. A toothpick should come out with moist crumbs.