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° F
Combine eggs and egg yolks in a small bowl and whisk lightly.
Place cocoa powder in a large mixing bowl.
Bring coffee (or water) to a vigorous boil and pour over cocoa powder. Whisk until combined.
Add chocolate to the hot coffee/cocoa mixture. Whisk until chocolate is melted.
Add melted butter and vegetable oil to the bowl. Whisk until incorporated.
Add eggs to the bowl and whisk until incorporated.
Add sugar to the bowl and whisk until incorporated.
Add flour and salt to the bowl and fold into batter using a rubber spatula. If pieces of flour are still visible, use a hand whisk to finish mixing the batter.
Pour brownie batter into prepared pan. Smooth top with an offset or rubber spatula.
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 (approximately 1 ½ hours).