• Preheat the oven to 350°F. Grease a 9-inch round cake pan and set aside.
• In a large bowl, combine the melted butter with both sugars. Add the egg and vanilla extract and stir to combine.
  ½ cup (113g) unsalted butter, ½ cup (100g) granulated sugar, ½ cup (100g) light brown sugar, 1 egg*, ½ teaspoon vanilla extract
• Add the flour, baking powder, and salt and stir to combine. Fold in the chocolate chips and M&Ms. Press the cookie dough into the prepared pan and bake for 20-25 minutes, or until edges look set and the cookie cake is slightly golden in color. Allow the cookie cake to cool in the pan completely before frosting.
  1 ½ cups (222g) flour*, ¾ teaspoon baking soda, ½ teaspoon fine sea salt, ⅓ cup (57g) semisweet chocolate chips, ⅓ cup Halloween M&Ms

Buttercream Frosting

• Using a hand mixer or a stand mixer fitted with the paddle attachment, beat the butter until smooth and creamy, about 4-5 minutes.
  ½ cup (113g) unsalted butter
• Add the powdered sugar and continue mixing until incorporated. Add the milk, one tablespoon at a time, until desired consistency is achieved. Use gel food coloring to tint the frosting before piping onto the cookie cake.
  1 ½ cups (180g) powdered sugar, 2-3 tablespoons milk of choice, gel food coloring