2/3 cup canola or any flavorless oil
2/3 cup natural unsweetened cocoa powder
1/2 cup all-purpose flour, plus more for dusting
1/4 teaspoon baking powder
1/2 teaspoon fine salt
3 large eggs
2/3 cup packed dark brown sugar
1 1/3 cups powdered sugar
1 teaspoon vanilla extract
Arrange a rack in the middle of the oven and heat to 325°F. Coat a 9-inch square baking pan with cooking spray, dust with flour, tapping out the excess, and set aside.
Place the oil into a microwave-safe medium bowl and heat on low power in 4 to 6 (5-second) bursts until it is warm but not hot. Add the cocoa powder and whisk until completely smooth and combined. Let sit for 4 or 5 minutes so the cocoa can bloom. Meanwhile, prepare the dry and wet ingredients.
Place the flour, baking powder, and salt in a small bowl and whisk to combine; set aside.
Place the eggs, powdered sugar, and brown sugar in a large bowl. (Alternatively, place in the bowl of a stand mixer fitted with the paddle attachment.) Beat on medium speed until fluffy and lighter in color, 2 1/2 to 3 minutes. Beat in the vanilla until just combined.
Add 1/2 of the cocoa mixture to the egg mixture and mix at medium-high speed until it is shiny and fully combined, about 5 minutes.
Add the flour mixture to the egg and cocoa mixture and mix at low speed until fully combined. Add the remaining cocoa mixture and and mix at medium-high speed until the batter is shiny and fully combined, about 1 minute. Transfer to the baking pan.
Bake for 20 to 24 minutes (you can allow it to bake for up to 30 minutes if you like a firmer brownie with some crisp edges). The brownies will pull away from the edges of the pan, but a cake tester or knife inserted in the middle will not come out clean. Let cool before cutting into 16 small squares.
Storage: These will keep in a closed container or wrapped in plastic at room temperature for up to 2 days.