Preheat oven to 350 degrees with the tray in the bottom rack. Cut 2 pieces of parchement paper to fit inside a 9x13 baking dish, 1 piece to fit vertically and the other piece to fit horizontally. Spray with non-stick spray, and I like to clap 2 of the edges down with large paper clips. Makes it easier when pouring in the brownie batter.

In a large mixing bowl, add cocoa powder, then boiling water. Whisk to combine. Then add finely chopped unsweetened chocolate. Whisk until melted. Add in melted butter and vegetable oil. Whisk to combine. Mixture may look "broken" or "curdled" at this point, that's ok. Add in the eggs and egg yolks. Whisk to combine. Add in vanilla and salt, whisk to combine. Add in sugar, whisk to combine. Last, add in all purpose flour and gently fold the flour using a spatula until just combined.

Pour brownie batter into baking dish, making sure to spread it to be an even layer. Bake in the oven for 30-35 minutes, or until an inserted toothpick comes out with a few fine crumbs. Remove from oven, and allow to cool in baking dish for 10 minutes. Then remove the brownies from the baking dish by lifting the parchement paper out, this will avoid overcooking the brownies. Allow to cool for at least 1 hour before cutting in to brownies.