Step 1: Preheat your oven to 375°F (190°C). Grease and flour a 9-inch round cake pan or line it with parchment paper for easy removal.
Step 2: In a large bowl, cream together the softened unsalted butter, granulated sugar, and packed light brown sugar using an electric mixer until light and fluffy. This should take about 2-3 minutes.
Step 3: Beat in the eggs one at a time, ensuring each is fully incorporated before adding the next. Stir in the vanilla extract. Scrape down the sides of the bowl to ensure everything is well combined.
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. Be careful not to overmix.
Step 6: Fold in the chocolate chips and any optional mix-ins (like chopped nuts) until evenly distributed throughout the dough. Reserve a few for topping if desired.
Step 7: Press the cookie dough evenly into the prepared cake pan. Sprinkle reserved chocolate chips over the top now for a visually appealing finish.
Step 8: Bake for 20-25 minutes, or until the edges are golden brown and a toothpick inserted into the center comes out with moist crumbs, not wet batter. The center might still look slightly soft; it will set as it cools.
Step 9: Remove the cookie cake from the oven and let it cool in the pan for at least 10-15 minutes before attempting to transfer it.
Step 10: Carefully invert the cake onto a wire rack, then flip it back onto another rack to cool completely. This helps prevent the bottom from becoming soggy.
Step 11: Once completely cool, decorate with your favorite frosting (buttercream is classic!) or toppings. Slice and serve. Store any leftovers in an airtight container.