Candy Bar Cookie Pie

For the cookie pie:
Generously grease a 9-inch pie dish and line the bottom with a round of parchment paper. Set aside.
With a hand mixer or stand mixer, beat butter with brown sugar and granulated sugar for several minutes, until light and fluffy. Add egg and vanilla extract, beat to combine.
In a separate bowl, combine flour, cornstarch, baking soda, and salt. With the mixer on low, slowly add the the dry ingredients, mixing until combined.
Using a rubber spatula or wooden spoon, stir in 1 cup of chopped candy bars. Press the dough evenly into the prepared dish. Sprinkle the remaining 1/2 cup of chopped candy bars onto the top of the dough, lightly pressing them down. Cover with plastic wrap and refrigerate for 1 hour.
Preheat oven to 350u0b0F. Remove plastic wrap and bake cookie pie for 18-20 minutes, until the edges are light golden brown and the center is set but still a little soft. Place on a cooling rack to cool completely.
For the chocolate frosting:
Beat butter, cocoa powder, powdered sugar, vanilla extract, and milk for several minutes. If necessary, add an additional tablespoon of milk to thin the frosting.
Using a pastry bag with a decorating tip, pipe the frosting around the outside edge of the cooled cookie. Decorate with M&Ms or chopped candy bars.
Recipe inspired by Baker by Nature's Halloween Candy Cookie Cake.