Preheat oven to 350°F. Line a 9x13 inch baking pan with foil, leaving about 1 inch of the foil extending over the edges of the pan. The extra foil will create handles that you can use to lift the Monster Cookie Bars from the pan. Spray foil with nonstick cooking spray. Set pan aside.

In the bowl of a stand mixer fitted with the paddle attachment, or in a large bowl with an electric mixer, cream butter, peanut butter and sugars on medium speed for about 3 minutes. Add in vanilla and eggs and mix until combined.

Stir together the oats and baking soda and gradually add the oats into the butter mixture until thoroughly incorporated. Stir in chocolate chips and M&M candies.

Spoon batter into prepared pan and spread into an even layer. If desired, top batter with an additional 1/4 cup M&M’s, pressing them lightly into the batter. Bake in preheated oven for 30-35 minutes. Remove pan to a cooling rack and cool completely before cutting into squares.