• Preheat oven to 350°F Spray a 9-inch pie dish or cake pan with nonstick spray. Set aside.
• In a large bowl using a hand-held mixer or stand mixer fitted with paddle attachment, beat the butter on medium speed until completely smooth and creamy, about 1 minute. Add the brown sugar and beat on medium speed until creamy. Mix in egg, egg yolk, and vanilla on medium-high speed until combined. Scrape down the sides and bottom of the bowl as needed.
• Add in the cornstarch, baking soda and salt and mix until combined. Then mix in the flour. Add in the chocolate chips and *1/2 cup of M&M's and gently fold in.
• Press the cookie dough evenly into the prepared pan. Add the rest of the M&M's on top. Bake for 25-30 minutes or until the cake is lightly golden brown. (If it begins to brown too much on the edges you may want to cover the cake loosely with aluminum foil.) Remove from the oven and set the pan on a wire rack to cool completely. Once cooled, use a sharp knife or metal spatula to loosen the sides of the cookie cake from the pan and transfer to a serving dish. (Or use can serve directly from the pan.)

Chocolate Frosting for Spiderweb

• In a medium mixing bowl, stir together the butter and cocoa powder until smooth. Then add in the powdered sugar. Mix together then add in the heavy cream or milk and vanilla. Once smooth add enough black food coloring to get desired black color. Pipe on chocolate frosting as a spiderweb using either a piping bag or ziplock bag with a small corner snipped,. Top with plastic spiders. Remove before serving. Slice and enjoy!
• Cookie cake remains fresh covered tightly at room temperature for up to 3 days.