Preheat oven to 350°.
Prepare a 9 x 13" baking pan with baking spray . I like to line my pan with foil and then spray it so that I can easily lift the brownies out.
In a double boiler, melt the chocolate and butter and set aside.
In a medium mixing bowl combine the flour, and baking powder.
Mix with a whisk to eliminate the lumps.
In a large mixing bowl or the bowl of a stand mixer combine the eggs, sugar, salt and vanilla.
Beat with a whisk until well aerated, about 5 minutes.
Add the melted chocolate and whisk to combine.
Stir in the dry ingredients using a rubber spatula.
Pour the batter into the prepared pan, spread the batter evenly.
Bake for 40-45 minutes or until a toothpick inserted into the center comes out clean.
Cool on a cooling rack for at least an hour.
Cut into squares.