1-First Step: Preheat your oven to 350°F (175°C). Proper temperature is key to ensuring the cookie cooks evenly without burning the edges before the center is done. While the oven heats up, grease a 12 to 14 inch pizza pan or a round baking sheet lightly. You can also line it with parchment paper for easier removal later, though greasing is usually sufficient for this size.

2-Second Step: In a large mixing bowl, combine 1 cup of softened unsalted butter and 1 cup of granulated sugar. Use a hand mixer or a stand mixer fitted with the paddle attachment to cream these together on medium speed. You want to beat them for about 2 to 3 minutes until the mixture is pale yellow and fluffy. This step incorporates air into the dough, which helps with the rise and texture. Scrape down the sides of the bowl to ensure everything is well mixed.

3-Third Step: Add the large egg and 2 teaspoons of vanilla extract to the butter and sugar mixture. Beat again on medium speed until the egg is fully incorporated. The mixture might look slightly curdled at this point, which is normal. The pure vanilla extract is essential here, not just for flavor but for that comforting aroma that fills the kitchen while baking. If you are interested in the specific advantages of using pure vanilla over imitation, you can read about the benefits of vanilla extract.

4-Fourth Step: In a separate medium bowl, whisk together the dry ingredients. This includes 2 1/2 cups of all-purpose flour, 1/2 teaspoon of baking soda, and 1/2 teaspoon of salt. Whisking these together ensures that the leavening agent and salt are evenly distributed throughout the flour, preventing any pockets of salty or bitter taste in the final cake.

5-Fifth Step: With the mixer on low speed, gradually add the dry flour mixture into the wet butter mixture. Mix only until just combined. It is crucial not to overmix at this stage, as developing too much gluten can make the cookie cake tough rather than tender. The dough will be soft and thick but should hold its shape when pressed.

6-Sixth Step: Transfer the dough to your prepared pizza pan. Since the dough is soft, the easiest way to spread it is to lightly grease your hands with butter or cooking spray. Press the dough outward from the center toward the edges, aiming for an even thickness of about 1/4 inch. Try to make the surface as level as possible so it bakes uniformly. If you want to add sprinkles to the dough, press them into the top now before baking.

7-Seventh Step: Place the pan in the preheated oven and bake for 18 to 22 minutes. The edges should start to turn a light golden brown, and the center should look set but slightly soft. Remember, the cookie will continue to cook slightly on the hot pan after you take it out of the oven, so do not overbake it if you want a soft texture.

8-Eighth Step: Remove the pan from the oven and set it on a wire rack. Let the giant cookie cool completely in the pan. This is the hardest part, but it is necessary. If you try to frost it while it is still warm, the buttercream will melt and slide right off. Cooling usually takes about an hour to an hour and a half. If you are in a rush, you can place the pan in the refrigerator for 20 to 30 minutes once it is no longer hot to the touch.

9-Final Step: While the cookie cools, prepare the frosting. In a clean bowl, beat 1/2 cup of softened butter until smooth. Gradually add 2 cups of powdered sugar, mixing on low speed until combined. Add 1 teaspoon of vanilla extract and 2 to 3 tablespoons of milk. Increase the speed to high and whip for 2 minutes until light and fluffy. Once the cookie is cool, spread the frosting generously over the top. You can pipe a border around the edge for a polished look or add sprinkles and candles. Slice into wedges and serve.