Preheat the oven to 356º F (180° C). Spread a little butter in a cast iron pan (if it is cast iron, it is better) of approximately 7.80 inches (20 cm) in diameter.
In a medium bowl, sift the flour with the cornstarch, cocoa powder, baking soda and salt.
In a large bowl, cream the butter with the two types of sugar with an electric mixer or hand whisk for 3 minutes until the mixture is light and fluffy.
Add in the egg with the vanilla extract and the red coloring and beat for 1 more minute until blended.
Add the flour mixture and mix using a rubber spatula until a smooth batter forms. Add the chocolate chips and integrate with the same spatula until they are incorporated throughout the batter.
Place the batter in the skillet and spread it with the spatula until it is even.
Bake the cookie for 20-25 minutes until firm and lightly browned on the edges but not quite in the center. Take out of the oven and let it cool down for about 5 minutes.
Serve the cookie with vanilla ice cream or chocolate sauce and eat while still warm.