Monster Cookie Bars

4.75 from 8 votes

Monster Cookie Bars are so easy to make, and full of delicious flavor. Such a fun treat to bake with the kiddos!

Prep Time20

Cook Time27

Total Time47

Servings: bars

Preheat your oven to 350 degrees Fahrenheit. Spray a 9 by 13 inch baking dish with cooking spray and set aside.
In a medium sized bowl, whisk together the flour, baking soda, baking powder, and salt until fully combined. Set aside.
1 cup all purpose flour, 1/2 teaspoon baking soda, 1/2 teaspoon baking powder, 1/4 teaspoon salt
In a large bowl with a hand mixer (or in a stand mixer fit with the paddle attachment) beat together the butter, brown sugar and granulated sugar, until light and fluffy. About three minutes. Then proceed to beat in the peanut butter until fully combined.
1 cup unsalted butter, 1 cup brown sugar, 1/2 cup granulated sugar, 1 1/2 cups creamy peanut butter
Beat the eggs into the butter/sugar/peanut butter mixture, one at a time. Finally, beat in the vanilla.
2 large eggs, 2 teaspoons vanilla extract
Add in the flour mixture all at once (see note 3) mixing it in on a very low speed until it just begins to combine and then up the speed just a little and mix in until the flour has just disappeared.
Finally, stir in the chocolate chips, M&Ms, and oats.
Dish the batter into the baking pan. It will be very sticky. Spray a spatula with cooking spray and use that to spread out the dough.
Bake for 25 to 27 minutes or until the edges of the bars are golden brown. Allow to cool completely before cutting into 24 equal squares.
Store in an airtight container for up to 1 week. See notes in the post about freezing.

To measure the flour, spoon it into the measuring cup and level off the top, rather than scooping it right from the flour container.
Both quick cooking and old fashioned oats (often sold as rolled oats) both work in this recipe. Just use what you have on hand. Keep in mind it will change the texture just a little bit because quick cooking oats are old fashioned oats broken down. It's just a matter of personal preference.
Most cookie recipes suggest that you mix in the flour a little at a time so that the flour does not fly everywhere and it suggest that you not over-mix. I recently read that you should add it all at once, mixing in slowly at first so it doesn't go everywhere, and then just mixing until the flour disappears. This lowers the risk of over stimulating the gluten which can lead to a dense cookie.