Start by making the homemade Cornflake Crack. Set aside to cool and then break into small pieces, perfect to fold into cookie dough.
Preheat oven to 350 degrees. In a large mixing bowl, cream together butter, brown sugar, and sugar for 4 minutes until fluffy. Scrape the sides of the bowl halfway through mixing. Add in eggs and vanilla and mix for 1 minute longer
Fold in flour, baking soda, and salt. Once the dry ingredients are barely mixed in, fold in the cornflake crunch. Be careful not to overmix it so you don't break up the cornflake crunch. Set aside 1 cup to place on the top after baking.
Scoop the dough onto parchment paper lined, light-colored baking sheets, spaced at least two inches apart.
Bake for 9-12 minutes or until the edges are a light golden color. Once you remove the oven, shape them into a circle by using a metal spatula to gently press any uneven edges toward the center of each cookie, shaping them into neat circles. Alternatively, place a cup over the cookie and rotate it in a circular motion to achieve a perfectly round shape.
Lightly press the remaining 1 cup of cornflake crunch onto the top of the cookies. This makes them look more gourmet and also add extra toffee crunch to the cookies.
Let cool on baking sheet for at least 5 minutes before removing to a cooling rack.