Preheat the oven to 350°F and place the racks in the top and lower thirds. Grease a 9”x13” baking tin with butter, line it with parchment so that there’s a bit of overhang on the sides, and then grease the parchment as well.
In a small bowl, whisk together the baking powder and flour. Set aside.
In a saucepan, melt butter over low heat. Turn off the heat and stir in chopped chocolate until combined. Mix in the vanilla and set aside to cool slightly.
In a medium bowl, whisk together eggs, sugars, oil and salt. Pour the butter and chocolate mixture into the egg mixture and whisk vigorously until it is smooth.
Whisk in the cocoa powder just until there are no lumps.
Fold in the flour and baking powder and give the batter a few more stirs after it all comes together. (This helps make the brownies chewy.)
Pour the batter into the prepared 9”x13” tin, spread evenly (an offset spatula helps), and bake for 40 minutes on the lower rack.
Remove from the oven and let cool in the tin on a wire rack. Once cooled, use the parchment to lift the brownies out. Cut brownies and serve.
