Preheat your oven to 350 degrees F.
Line a baking dish with parchment pray or spray with nonstick baking spray.
In a medium bowl, mix together flour, baking soda and salt.
In a separate bowl (I used my Kithchen Aid) mix together butter, brown sugar and granulated sugar until creamed together.
Add in the eggs and vanilla to the butter sugar mixture, mixing well.
Add the dry ingredients (flour mixture) into the wet ingredients, and stir until combined.
Sprinkle in the chocolate chips or M &Ms
Spread the cookie dough into the prepared baking dish, pressing down until firm.
Bake until golden brown (about 20-25 minutes).
While the cookie dough bakes, unwrap your Halloween candies and chop or break into chunks.
When the cookie dough is done baking, remove from oven. Press the chocolate pieces into the top of the cookie while still warm. We had leftover googly eye sprinkles so I sprinkled those on as well.
Allow to completely cool, then cut and serve.