Make the cookie half

1. Preheat oven to 350°F (180°C). Prepare a 10-inch cake pan with parchment paper in the bottom and baking spray on the sides. Set aside.
2. Combine the flour, baking soda and salt in a medium sized bowl and set aside.
3. Cream the butter and sugars together in a large mixer bowl on medium speed until light in color and fluffy, 2-3 minutes. You may need to scrape down the sides of the bowl a few times to make sure it’s all incorporated. You should be able to see the change in color and texture and know it’s ready. Do not skimp on the creaming time.
4. Add the egg and vanilla extract and mix until well combined.
5. Add the dry ingredients to the butter mixture and mix until the dough is just well combined. Do not over mix. Once it’s well combined, use a rubber spatula to help it come together to form a more cohesive ball.
6. Gently stir in the chocolate chips.
7. Press the cookie dough evenly into one half of the prepared cake pan. Set aside.

Make the brownie half

1. Add the flour, cocoa powder, baking powder and salt to a medium sized bowl and set aside.
2. Add the oil, sugar and vanilla extract to large mixing bowl and mix together until well combined.
3. Add the eggs and mix until well combined.
4. Add the dry ingredients and mix until well combined, but don’t over mix.
5. Add the brownie batter to the other side of the pan, next to the cookie side, and spread evenly. Bake for 18-24 minutes, or until the top of the cookie is lightly browned and a toothpick inserted into the brownie comes out clean or with just a few moist crumbs. If it starts to brown too much, loosely cover with foil. Don’t over bake. It may seem a little underdone when it first comes out of the oven, but it will firm up as it cools.
6. Remove from the oven and allow to cool completely in the pan to make it easier to remove from the pan later. If you want to speed up the cooling, you can put it I the fridge for a bit.

Decorate

1. Once fully cooled, flip the cake out onto a flat plate, cardboard circle or your hand (which is what I do) and then flip it back over onto the serving plate/platter.
2. To make the buttercream, add the butter to a large mixer bowl and beat until smooth.
3. Add about half of the powdered sugar and the cocoa powder and mix until well combined and smooth.
4. Add the vanilla extract and 1 tablespoons of cream and mix until well combined and smooth.
5. Add the remaining powdered sugar and mix until well combined and smooth.
6. Add additional heavy cream, as needed, to get the right buttercream consistency.
7. Add the buttercream to a piping bag fitted with your preferred piping tip. I used Ateco 847. Pipe the buttercream around the outer edge of the cake, or decorate as desired. Serve.
8. Store in an airtight container. It can be kept at room temperature for up to 48 hours, then the buttercream should be refrigerated. Best if eaten within 3-4 days.