Preheat the oven to 175 C. Grease an 8" square pan and set aside.
In a bowl placed over a pot of simmering water, melt the butter, chocolate and cocoa until you have a smooth mixture. Do not overheat the mixture. If there are still a few lumps of chocolate, take the bowl off the heat and stir to melt fully. Let this cool while you get the rest of the batter ready.
Sift the flour, baking powder and salt, if using, in a bowl and set aside.
Beat the eggs, sugar and vanilla in a large bowl till pale, about 4 minutes. This is where you're ensuring a crackly 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 stir until well combined. Fold in the chocolate chips.
Pour into the prepared dish, smoothen the top (the batter doesn't spread much) and bake for 15 to 20 minutes till a toothpick poked in the center comes out with only a few moist crumbs. The top will feel a little soft, that's ok, it will firm up as the brownies cool down. Over baking will lead to dry brownies which are never fun!
Slice into squares once completely cooled. Store at room temperature in an airtight tin for 3 to 4 days, after which transfer to the fridge or freezer, especially in humid environments. Happy baking!