Beat together butter and the sugar until smooth and well mixed. Add eggs and vanilla extract, mix well.
In a separate bowl mix together flour, baking soda, and salt. Slowly add to butter mixture mixing well. Add the M&Ms and chocolate chips and mix well, again.
Place the batter into the 9x13 pan that is lined with parchment paper. Pat down until smooth and even. Top with extra M&Ms and chocolate chips.
Bake for approximately 40 minutes or until cooked through. You will want to put foil on top of the cookies 2/3 of the way through the baking process to avoid the cookie bars from getting too brown. Enjoy!