For the Cookie Cake

1. Preheat oven to 350°F (176°C). Grease the sides of a 9×13-inch cake pan and place parchment paper in the bottom.
2. In a medium-sized bowl, combine the flour, baking soda and salt.
3. In a large mixer bowl, cream the butter and sugars together until light and fluffy, about 2-3 minutes.
4. Add the eggs one at a time, mixing just until well combined before adding the next.
5. Add the vanilla extract and mix until well combined.
6. Add the dry ingredients and mix just until well combined. Dough will be thick and sticky.
7. Gently fold in the chocolate chips.
8. Spoon the cookie dough into the prepared pan and press the dough evenly into the cake pan. I use my offset spatula to spread it around in the pan, since it’s sticky.
9. Bake for 18-23 minutes, or until the top of the cookie is just beginning to brown on top. To make this cookie cake in a 10×15-inch pan, bake at 350°F for about 15 minutes, or until it just begins to brown on top.
10. Remove from oven and allow to cool completely in the cake pan, then transfer to serving plate. I find it can help to refrigerate the cake after it has cooled to firm it up before removing from the pan. It helps it stay together while you remove it from the pan. To remove this cookie from such a large pan, I use a cooling rack and a cardboard cake rectangle (two cooling racks would also work). I place the cooling rack (lined with parchment paper) against the top of the cake pan, then flip it over. Immediately and quickly place the cardboard cake rectangle on top of the cookie cake (which is the bottom) and flip the whole thing over using the cooling rack. Remove the cooling rack from the top of the cake.

For the Frosting

1. Add the butter to a large mixer bowl and beat until smooth.
2. Add about half of the powdered sugar and mix until well combined and smooth.
3. Add the cocoa powder, vanilla extract and two tablespoons of water or cream and mix until well combined and smooth.
4. Add the rest of the powdered sugar and mix until smooth. Add more water or cream to get the right consistency.
5. Add the buttercream to a piping bag fitted with a piping tip (I used Ateco 847) and pipe swirls of frosting around the outer edge of the cake.
6. Store cookie cake in an airtight container or cover well. Cookie cake is best if eaten within 3-4 days.