Preheat oven to 350. Spray a 9-inch pan with non-stick spray.
Cream butter and sugar together until light and fluffy, about 2-3 minutes. Mix in egg and vanilla extract until combined. On low speed, add flour, cornstarch, baking soda and salt and mix until combined. Stir in 1 1/4 cups chocolate chips.
Spread the cookie dough into the pan, I use a piece of plastic wrap to keep it from sticking to my hands. Sprinkle with remaining 1/4 cup chocolate chips.
Bake for 20-25 minutes or until the edges are slightly golden and the center is set (the center will be set, but not baked through).
Remove from oven and allow to cool most of the way. Run a sharp knife to loosen the sides before turning it out onto a cooling rack or cake plate and cool completely before decorating.