Step 1: Preheat your oven to 350°F (175°C). Lightly grease a 12-inch round pizza pan or a 9x13-inch baking dish with butter or non-stick spray. If using a pizza pan, you may want to line it with parchment paper for easier removal, leaving an overhang to lift it out.
Step 2: In a large mixing bowl, using an electric mixer, cream together the softened unsalted butter, granulated sugar, and brown sugar on medium speed until light and fluffy, about 2-3 minutes. This step is crucial for incorporating air and achieving a tender texture.
Step 3: Beat in the eggs one at a time, mixing well after each addition. Stir in the vanilla extract until just combined. Scrape down the sides of the bowl to ensure everything is evenly incorporated.
Step 4: In a separate medium bowl, whisk together the all-purpose flour, baking soda, and salt. Gradually add the dry ingredients to the wet ingredients, mixing on low speed until just combined. Be careful not to overmix; overmixing can lead to a tough cookie cake.
Step 5: Fold in the chocolate chips (and any other mix-ins like nuts or additional chocolate) until evenly distributed throughout the dough. Reserve a small handful for sprinkling on top if desired.
Step 6: Press the cookie dough evenly into the prepared pizza pan or baking dish. You can use your hands or the back of a spoon. Make sure the dough is spread to the edges. Sprinkle the reserved chocolate chips on top.
Step 7: Bake for 20-25 minutes, or until the edges are golden brown and the center is set but still looks slightly soft. The cook time will vary slightly depending on your oven and the thickness of your cookie cake. For a chewier cookie cake, err on the side of slightly underbaking.
Step 8: Remove the cookie cake from the oven and let it cool completely in the pan on a wire rack before frosting and serving. Cooling completely allows the cookie to set properly and prevents your frosting from melting.
Step 9: Once cooled, decorate your cookie cake! A simple buttercream frosting piped around the edges and a fun message in the middle is classic. Get creative with sprinkles, candies, or even a drizzle of chocolate ganache.
Step 10: Slice and serve! This cookie cake is best enjoyed warm or at room temperature.