Preparation Steps

• Preheat oven to 350°F. Line a 9-inch cake pan with parchment paper on the bottom and spray the sides with baking spray.
• In a medium bowl, whisk together flour, cornstarch, baking soda, and salt until combined.
• In a large bowl, cream together the butter and both sugars on medium speed until light and fluffy, about 2-3 minutes.
• Add the egg and vanilla extract to the creamed mixture and mix until fully incorporated.
• Gradually add the dry ingredients to the wet mixture and mix until just combined. Use a rubber spatula to form the dough into a cohesive ball.
• Fold in the semi-sweet chocolate chips evenly into the dough.
• Press the dough evenly into the prepared cake pan. Optionally, press a few extra chocolate chips on top.
• Bake for 18-20 minutes or until the edges turn golden and the center is set.
• Remove from oven and allow the cookie cake to cool completely in the pan before transferring to a serving plate.
• To make the chocolate buttercream: Beat the butter in a large bowl until smooth. Add half the powdered sugar and mix well. Add cocoa powder, vanilla extract, and 1 tablespoon of heavy cream; mix until smooth. Add remaining powdered sugar and mix until fluffy, adding more cream if needed.
• Pipe chocolate buttercream swirls around the edge of the cooled cookie cake and store the cake in an airtight container. Serve at room temperature for best texture.