Preheat oven to 350°F. Spray a 9X13 pan with baking nonstick spray. Line with parchment paper on the bottom and 2 sides. Spray again.
In a mixing bowl, sift the flour, cocoa powder, cornstarch, and salt. Using a mixer with a whisk attachment, beat the eggs, egg yolk, and sugar together. Beat on high for 5 minutes. The sugar/eggs will get be very light and fluffy.
While the eggs are mixing, melt the butter in the microwave. Then, let it slightly cool. Once the eggs are done mixing, add in the oil, melted butter, and vanilla. Mix on low until combined. Take off mixer.
Fold in the dry ingredients. Fold until it is completely combined, but be gentle so none of the air from the eggs deflates. Fold in the chocolate chips.
Pour batter into the pan. Bake for 60-70 minutes. The brownies are done baking the edges are set, but the middle is very slightly underdone.
Let it sit for 25 minutes before forming into the crust. Spray a 9 inch spring form pan with baking non-stick spray. Place a parchment paper on the bottom and spray again.
Use gloves and form the warm brownies into the crust. Use only the middle of the brownies and use only ¾ths of the tray. It should go halfway up the pan. Compact with your hands. Then, let it sit while you make the batter.