Preheat oven to 350*F.
Combine dry ingredients (Flour, Cocoa Powder, Baking Soda, Cornstarch and Salt) in large mixing bowl.
Whisk dry ingredients until combined.
Add Butter + Sugar in a separate large mixing bowl.
Whisk Butter with Sugar until creamed (approx. 60 seconds).
Add other wet ingredients (Eggs, Vanilla Extract) to creamed Butter + Sugar and whisk for 30 seconds each until combined.
Add wet ingredients into bowl with dry ingredients and fold until just combined.
Generously grease 9x9 cake pan with cooking spray, butter or oil.
Add brownie batter to cake pan and spread until it forms even layer.
Place cake pan oven and bake for 25-30 minutes.
Allow brownies to cool for at least 30 minutes before cutting and serving.