Preheat the oven to 350 degrees and line an 8x8 cake pan with aluminum foil, leaving tabs to help remove the brownies after baking; spray the foil with cooking spray and set aside.

In a medium-sized bowl, whisk the flour, baking powder and salt until well combined; set aside.

Meanwhile, melt the chocolate and butter in a large bowl, over a double boiler; once fully melted, remove from the heat.

Add the oil and stir to combine.

Add the sugar and light brown sugar and mix to combine.

Add the eggs, egg yolk and vanilla, and whisk until the batter is glossy, about 2 minutes.

Add the dry ingredients and mix with a rubber spatula, just until combined.

Pour the batter into the prepared cake pan and bake until a cake tester shows moist crumbs, about 35 minutes.

Cool in the pan for 15 minutes before transferring the brownies to a cooling rack to cool completely.

Carefully remove the foil and cut into 9 squares.