Step 1: Preheat your oven to 350°F (175°C). Grease a 9-inch round cake pan or springform pan and line the bottom with parchment paper.
Step 2: In a large bowl, cream together the softened butter, brown sugar, and granulated sugar until light and fluffy, about 2-3 minutes.
Step 3: Beat in the egg and vanilla extract until well combined and smooth.
Step 4: In a separate medium bowl, whisk together the flour, cornstarch, baking soda, and salt.
Step 5: Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Do not overmix.
Step 6: Fold in the chocolate chips by hand using a spatula.
Step 7: Press the cookie dough evenly into the prepared pan. Add a few extra chocolate chips on top for a professional look.
Step 8: Bake for 20-25 minutes, or until the edges are lightly golden brown but the center still looks slightly soft.
Step 9: Remove from the oven and allow to cool completely in the pan before removing and decorating with frosting.