Preheat your oven to 350°F (175°C). Grease a 9-inch springform pan with cooking spray and line the bottom with parchment paper. Set it aside.
In a medium bowl,combine flour, baking soda, and salt. Mix well, and set aside.
2 cups all-purpose flour, 3/4 teaspoon baking soda, 1/2 teaspoon salt
In a separate bowl, beat the butter, brown sugar, and granulated sugar for about 3-5 minutes until light.
1/2 cup salted butter,, 1/2 cup light brown sugar, 1/2 cup granulated sugar
Add the eggs one at a time to the butter mixture and beat for 3 minutes until pale and fluffy. Add the vanilla extract.
2 large eggs, 2 teaspoons pure vanilla extract
Slowly add the flour mixture to the wet mixture, combining until everything is well incorporated. Stir in the chocolate chips.
1 cup semisweet chocolate chips
Transfer the batter to the prepared pan and smooth the top with a spatula. Sprinkle the remaining 2 tablespoons of chocolate chips over the top.
Bake for 23–25 minutes, or until the cookie cake turns a light golden brown color.
Once done, remove the cookie cake from the oven and let it cool for 10 minutes. Run a butter knife around the sides of the cake, then slowly release the springform pan and transfer it to a cooling rack.
Meanwhile, prepare the chocolate buttercream by beating butter, cocoa powder, milk, and vanilla extract using a hand mixer. Slowly add the powdered sugar and beat until smooth and creamy for 3-5 minutes. Transfer the chocolate buttercream to a piping bag with a star nozzle.
4 Tablespoons salted butter, 2 Tablespoons natural unsweetened cocoa powder, 1-2 Tablespoons milk, 1/2 teaspoon vanilla extract, 1 cup powdered sugar
Pipe the chocolate buttercream around the edge of the cookie cake and sprinkle rainbow sprinkles on top.
2 Tablespoons rainbow sprinkles
Once done, slice the chocolate chip cookie cake and serve.