Homemade Cookie Cake

1 . Stage

Beat brown sugar, unsalted butter, and white sugar together in a bowl using an electric mixer until light and fluffy, 3 to 4 minutes. Mix in egg and 2 teaspoons vanilla extract until smooth. With the mixer on low speed, add flour, baking soda, and salt and blend until batter is just mixed. Fold chocolate chips into batter. Batter will be thick. Chill in the refrigerator at least 30 minutes to overnight.

2 . Stage

Preheat the oven to 350 degrees F (175 degrees C). Line a 9-inch cake pan with parchment paper.

3 . Stage

Spread batter into the prepared cake pan.

4 . Stage

Bake in the preheated oven until edges are golden brown, about 20 minutes. Slightly cool cake in the pan before transferring to a wire rack to cool completely, about 30 minutes.

5 . Stage

Beat shortening and butter together in a bowl using an electric mixer until smooth. Slowly beat in 3 cups of confectioners' sugar until smooth. Mix water and 1 teaspoon vanilla extract into confectioners' sugar mixture; add remaining confectioners' sugar and mix until buttercream is smooth. Add more water to thin, if needed.

6 . Stage

Spread or pipe buttercream onto cookie cake.