Sieve the flour, baking powder and salt in a bowl and set aside.
In a bowl placed over a pot of simmering water, melt the butter, peanut butter, chocolate and cocoa until you have a smooth mixture. If a few lumps of chocolate remain, take the bowl off the heat and stir till melted through, do not over heat the mixture. Let it cool for a few minutes.
Meanwhile, preheat the oven to 175 C. Grease an 8x8 baking dish and line with baking paper, leaving a little overhang for easy removal. Grease the paper too.
Beat the eggs, sugar and vanilla in a large bowl till pale and thickened, about 4 minutes. This is where you’re ensuring a crust forms, so beat away! An electric mixer will get the best results.
Add the cooled chocolate mixture to the egg mixture and beat again till combined.
Finally add the flour mixture and fold gently to combine. The batter will be thick, almost like frosting!
Spoon into the prepared dish, and smoothen the top. Bake for 20 minutes, or until a toothpick poked in the center comes out with moist crumbs but no wet batter. Brownies continue to cook as they cool, so don't overbake them.
Let the brownies cool in the tin for 20 minutes, then remove using the overhang of the baking paper and set on a wire rack. Slice into 16 equal pieces when completely cool. Store in an airtight tin at room temperature for 4 to 5 days, or in the fridge for 10 days. You can even freeze them for a month. Happy baking!