Preheat oven to 350° F. Line a baking sheet with a non-stick silicone mat and set aside.
Chop up your candy bars as small as you can and pour into a small bowl, candy dust and all. Set aside.
In a small bowl, whisk together flour, baking soda and salt. Set aside.
In a large bowl using a stand or hand mixer, cream together butter, granulated sugar and brown sugar. Add egg and vanilla, mix until well combined.
Add dry ingredients to wet ingredients and mix until just combined. Add chopped candy bars and M&Ms and stir until combined. If you feel like the dough has gotten too warm, wrap it in plastic wrap and toss it in the fridge for a few hours to let it firm up again. Okay, don't actually toss it - you might knock a carton of milk over or something.
Using a medium-sized cookie scoop, place dough onto prepared baking sheet an inch apart.
Bake for 12 minutes, or until the edges start to turn gold.
Let cool on baking sheet for a few minutes, then move them to a cooling rack to cool completely. Enjoy!