Ingredients:

  • 3/4 cup unsalted butter, melted and cooled
  • 3/4 cup dark brown sugar, packed
  • 1/4 cup granulated sugar
  • 1 large egg, room temperature
  • 1 large egg yolk, room temperature
  • 2 teaspoons vanilla extract
  • 2 cups all-purpose flour
  • 1 teaspoon cornstarch
  • 1 teaspoon baking soda
  • 1/2 teaspoon kosher salt
  • 1 1/4 cups semi-sweet chocolate chips
  • 1/2 cup unsalted butter, softened (for frosting)
  • 1 1/2 cups powdered sugar
  • 2 tablespoons cocoa powder
  • 1.5 tablespoons heavy cream
  • 1 pinch salt

Instructions:

  1. Preheat your oven to 350°F (175°C). Grease a 9-inch round cake pan or springform pan and line the bottom with parchment paper.
  2. In a large mixing bowl, whisk together the melted butter, brown sugar, and granulated sugar until fully combined and smooth.
  3. Add the whole egg, egg yolk, and vanilla extract. Whisk vigorously until the mixture is lightened in color and well emulsified.
  4. Sift in the all-purpose flour, cornstarch, baking soda, and kosher salt. Use a rubber spatula to fold the dry ingredients into the wet until just combined.
  5. Fold in the semi-sweet chocolate chips. Transfer the dough to the prepared pan and press into an even layer.
  6. Bake for 20 minutes, or until the edges are golden brown and the center is set but still soft. Do not overbake. Allow to cool completely in the pan.
  7. Prepare the buttercream by beating softened butter, powdered sugar, cocoa powder, cream, and salt until fluffy. Pipe a decorative border around the edges of the cooled cookie cake.