Spray inside of 13" x 9" pan with baking spray, line bottom with parchment paper. Alternatively use a flexible silicon pan (no spray or parchment needed).
Preheat oven to 350℉ (180℃)
Combine eggs and egg yolks in a small bowl and whisk lightly. Set aside for later.
3 Large Eggs, 3 Large Egg Yolks
Place cocoa powder in a large mixing bowl.
½ Cup Cocoa Powder, Unsweetened
Bring coffee (or water) to a vigorous boil and pour over cocoa powder. Whisk until combined.
1 Cup Brewed Coffee (alternatively use water)
Add chocolate to the hot coffee/cocoa mixture. Whisk until chocolate is melted.
½ Cup Chocolate, bittersweet
Add melted butter and vegetable oil to the bowl. Whisk until incorporated.
6 Tablespoons Unsalted Butter, 1 Cup Vegetable or Canola Oil
Add eggs to the bowl and whisk until incorporated.
Add sugar to the bowl and whisk until incorporated.
3 ¾ Cups Granulated Sugar
Add flour and salt to the bowl and fold into batter using a spatula. If pieces of flour are still visible, use a hand whisk to finish mixing the batter.
3 Cups All Purpose Flour, 1 teaspoons Salt
Pour the brownie batter into the prepared pan and use an offset or rubber spatula to smooth the top. Note: The batter will be thin, so it will spread easily.
Bake for 20 minutes, rotate pan and bake an additional 20 minutes (40 minutes total).
Remove pan from the oven and set on a cooling rack. Allow the brownies to cool to room temperature before unmolding (approximately 1 ½ hours).