Preheat your oven to 350 degrees F. Lightly coat a pizza pan with non-stick cooking spray.

In medium bowl, mix flour, cornstarch, baking soda and salt together. Set bowl aside.

Cream butter, brown sugar, and granulated sugar together on medium speed until well combined (about 2 minutes). Add egg; beat for 1 minute on high. Add vanilla extract, and beat well to combine.

Add the flour mixture to the wet ingredients. Slowly mix on low until they are fully combined. Stir in the chocolate chips.

Place the dough onto prepared pizza pan. Use a rubber spatula or your clean fingers to spread and flatten out the thick dough until the dough just about reaches the edges of pan.

Bake cookie for 22-25 minutes. When done, the cookie should be lightly browned on top. If you want crispy edges on the cookie, let it bake a couple minutes longer. When done, remove pan to a wire rack and let cookie cool (still on the pan).

Place semi-sweet chocolate chips and white chocolate chips in two separate bowls. Add 1 teaspoon vegetable shortening to each bowl. Microwave each on high for 30 seconds. Stir until smooth. If necessary, heat additional 15 seconds, then stir, until smooth. Do not over cook as the chocolate can burn. Drizzle the chocolate over the cooled cookie in a decorative pattern. Let chocolate firm up on pizza before wrapping as a gift or slicing. For packaging, place cookie on parchment paper (cut to fit) and place cookie "pizza" inside a clean pizza box.