1. For best texture and flavor, optionally refrigerate cookie dough wrapped tightly for 1 to 3 days. Before baking, let dough soften on the counter about 1 hour.
2. Bring butter and eggs to room temperature. Soften butter until it leaves an imprint when pressed with your thumb.
3. In a bowl, whisk together flour, cornstarch, baking soda, and salt; set aside.
4. Using a stand mixer with paddle attachment or an electric hand mixer, cream softened butter with both sugars for about 2 minutes until smooth and fluffy.
5. Add eggs one at a time (or both at once if preferred), mixing 30 to 45 seconds until combined. Beat in vanilla extract.
6. Slowly add the flour mixture on low speed, mixing until just combined; the dough may seem crumbly but will come together.
7. Fold in chocolate chips with a spatula or mix on low speed.
8. Wrap dough in plastic or parchment paper and refrigerate 1 to 3 days, or bake immediately if skipping chilling.

9. Preheat oven to 350°F (175°C). Grease a 14.5 to 15-inch rimmed pizza pan or line with parchment paper. A rimmed baking sheet or 14-inch round cake pan can be used as alternatives, adjusting dough quantity and baking time as needed. Avoid pans with holes to prevent dough spillover.
10. Break dough into chunks and press evenly into pan up to edges. Press extra chocolate chips on top if desired.
11. Bake centered in the oven for 16 to 25 minutes — about 16 minutes for a softer, less browned center or up to 25 minutes for a more fully set cookie. Adjust baking time if using different pan sizes or thicknesses.
12. Remove from oven and cool on a wire rack for about 1 hour until set and cool enough to frost.

Frosting Instructions:
1. Beat softened butter on medium speed until creamy, about 1 to 2 minutes, scraping bowl sides as needed.
2. Gradually add powdered sugar starting on low speed, then increase to medium, beating for 1 to 2 minutes until smooth.
3. Mix in heavy cream, vanilla extract, and salt until well combined and pipeable. Add gel-based food coloring if desired for vibrant colors.
4. Frost cookie cake using piping bags with decorative tips or improvise with a plastic bag.