Chocolate Chip Cookie Cake

My favorite way to eat a chocolate chip cookie when its the size of a cake! Decorate with frosting slice and serve.
Ingredients
34 cup 12 Tbsp 170g unsalted butter softened to room temperature
1 cup 200g packed light or dark brown sugar
1 large egg 1 egg yolk
2 teaspoons pure vanilla extract
2 cups 250g allpurpose flour spooned leveled
2 teaspoons cornstarch aka cornflour
1 teaspoon baking soda
12 teaspoon salt
1 and 12 cup 225g semisweet chocolate chips
optional chocolate buttercream for topping
Instructions

Preheat oven to 350F 177C. Spray a 9inch pie dish or 9inch round cake pan with nonstick spray. Set aside.
In a large bowl using a handheld mixer or stand mixer fitted with paddle attachment beat the butter for 1 minute on medium speed until completely smooth and creamy. Add the brown sugar and beat on medium speed until creamy about 1 minute. Mix in egg egg yolk and vanilla on mediumhigh speed until combined. Scrape down the sides and bottom of the bowl as needed.
In a separate bowl combine flour cornstarch baking soda and salt. On low speed slowly mix into the wet ingredients until combined. The cookie dough will be quite thick. Add 1 and 14 cups chocolate chips and mix for about 5 seconds until evenly disbursed.
Press the cookie dough evenly into the prepared pan. Bake for 2025 minutes or until the cake is lightly golden brown could be up to 30 minutes depending on your oven. Use a toothpick to test for doneness. You may want to cover the cake loosely with aluminum foil after 15 minutes to avoid heavy browning around the edges. Remove from the oven and set the pan on a wire rack to cool completely. Once cooled use a sharp knife or metal spatula to loosen the sides of the cookie cake from the pan and transfer to a serving dish. Or use can serve directly from the pan.
The chocolate buttercream is optional. Instead decorate with whipped cream or top with vanilla ice cream.
Decorate the cooled cookie cake with frosting and remaining 14 cup chocolate chips. Depending how much frosting you use you may have some leftover. I used a Wilton 1M tip. Cookie cake remains fresh covered tightly at room temperature for up to 3 days.