Preheat your oven to 350°F (175°C). Grease a 9-inch round cake pan or line it with parchment paper.
Mix dry ingredients: In a medium bowl, whisk together 2 ½ cups of all-purpose flour, 1 teaspoon of baking soda, and ½ teaspoon of salt.
Cream the butter and sugar: In a large mixing bowl, beat 1 cup of softened unsalted butter with 1 cup of brown sugar and ½ cup of granulated sugar until light and fluffy, about 2-3 minutes.
Add eggs and vanilla: Add 2 large eggs, one at a time, beating well after each addition. Stir in 2 teaspoons of vanilla extract.
Combine with dry ingredients: Gradually add the dry ingredients to the wet mixture, mixing just until combined. Avoid overmixing.
Add mix-ins (optional): Fold in 1 cup of chocolate chips, nuts, or any other desired mix-ins.
Bake the cookie cake: Spread the dough evenly in the prepared pan. Bake for 20-25 minutes or until the edges are golden and a toothpick inserted into the center comes out clean.
Cool and decorate: Let the cookie cake cool in the pan for 10 minutes, then transfer it to a wire rack to cool completely. Once cooled, decorate with frosting, sprinkles, or any toppings of your choice.