Step 1: Preheat your oven to 350°F (175°C). Grease a 12-inch round pizza pan or a 9x13 inch baking pan with butter or cooking spray. You can also line it with parchment paper for easier removal.
Step 2: In a large mixing bowl, cream together the softened unsalted butter, granulated sugar, and light brown sugar until the mixture is light and fluffy. This usually takes 2-3 minutes with an electric mixer. Scrape down the sides of the bowl as needed.
Step 3: Beat in the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.
Step 4: In a separate medium bowl, whisk together the all-purpose flour, baking soda, and salt.
Step 5: Gradually add the dry ingredients to the wet ingredients, mixing on low speed until just combined. Do not overmix. Fold in the chocolate chips by hand, saving a few to sprinkle on top.
Step 6: Press the cookie dough evenly into the prepared pan. If using a pizza pan, ensure the dough goes right to the edges. Sprinkle the reserved chocolate chips on top. Bake for 18-25 minutes, or until the edges are golden brown and the center is set but still looks slightly soft.
Step 7: Remove the cookie cake from the oven and let it cool completely in the pan on a wire rack before frosting and serving. Once cool, frost with your favorite buttercream and decorate as desired.