In your trusty stand mixer, blend the melted butter, granulated sugar, light brown sugar, and vanilla extract until creamy. Add the room temperature eggs and mix until well incorporated.
Slowly introduce the flour, cornstarch, cocoa powder, baking soda, and salt. Mix until everything dances together in perfect harmony.
Preheat the oven to 350°F. Grease an 11-inch springform pan, line the bottom with parchment paper, and spread your cookie dough evenly. Bake for 25-30 minutes until the edges and top are splendidly set. Allow it to cool completely.