Step 1

Arrange a rack in the middle of the oven and heat the oven to 325°F. Coat a 9-inch square baking pan with cooking spray. Dust the pan with flour, tap out the excess, and set aside.

Step 2

Place the oil into a microwave-safe medium bowl and heat on low power in 4 to 6 (5-second) bursts until 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.

Step 3

Place the flour, baking powder, and salt in a small bowl and whisk to combine; set aside.

Step 4

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.) Using an electric hand mixer, beat on medium speed until fluffy and lighter in color, 2 1/2 to 3 minutes. Beat in the vanilla until just combined.

Step 5

Add 1/2 of the cocoa mixture to the egg mixture and mix at medium-high speed until 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 shiny and fully combined, about 1 minute. Transfer to the baking pan and spread into an even layer.

Step 6

Bake for 20 to 24 minutes (you can 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 squares.