• Preheat the oven to 350 degrees Fahrenheit. Spray an 8 inch cake pan with nonstick spray then set aside. Cut a circle out of parchment paper slightly smaller than the inside of the pan. Set it in the bottom of the pan and spray with nonstick spray.
• In the bowl of a stand mixer cream together the butter and both sugars on medium speed until light and fluffy - about 5 minutes. Add the egg and beat again until incorporated. Scrape down the sides of the bowl with a spatula.
• In a medium bowl combine the flour, baking soda, and salt. Stir with a small whisk or fork then pour the flour mixture into the butter/egg mixture and beat until well combined.
• Add the chocolate chips to the cookie dough and turn the mixer on low until the chips are evenly dispersed throughout the batter.
• Scrape the batter into the greased cake pan and spread evenly throughout the pan. Bake for 22 minutes. Let the cookie cool completely before removing or frosting.
• To remove the cookie from the pan: Let the big cookie cool until it's only slightly warm. Place a large flat cutting board over the top of the cake pan.
• While holding the cake pan and the cutting board together flip them over. Remove the cake pan. Now you will have a cookie cake on a cutting board that's upside down.
• Place whatever plate or serving platter you're using on top of the upside down cookie. The bottom of the plate should be facing you. Carefully hold the cutting board and plate together then flip one more time.

For the buttercream:

• Cream the butter and ½ cup of the powdered sugar for 3 minutes on medium speed.
• Add 1 ¼ cup more of powdered sugar, the heavy cream, vanilla, and a pinch of kosher salt. Beat for 3 more minutes on medium speed. Stop the mixer halfway through and scrape down the sides of the bowl with a spatula to make sure everything gets incorporated.
• Scrape the buttercream into a piping bag and pipe onto the cooled cookie cake. You don't have to use all of the buttercream on the cake! I typically use half of this recipe and place the rest in the fridge for another use.