Preheat the oven to 350F (180C) degrees. Line the bottom of a 9-inch springform pan with parchment paper and grease the edges. Or lightly grease a 9-inch pie plate. I like to use a springform pan for this recipe.
In a medium bowl sift together the flour, cocoa, cornstarch, baking soda and salt. Whisk together.
In a separate large bowl beat together the butter, granulated sugar and brown sugar until creamed.
Beat the egg, additional egg yolk, vanilla extract and red food coloring into the butter mixture.
Add the flour mixture to the butter mixture. Start with the mixer on a low speed and beat together until combined.
Stir the chocolate chips into the batter.
Spoon the batter into the prepared pan. Spread into an even layer. Or alternatively, use a piece of wax paper to press the batter down into an even layer (be sure to remove the wax paper before baking.
Bake in the preheated oven for about 30-35 minutes, or until the top looks set and an inserted toothpick comes out clean or with a few cookie crumbs.
Remove from the oven and cool the cookie cake fully (keep in the pan as the cookie cake cools).