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Easy Monster Cookie Bars

When you make these Easy Monster Cookie Bars, you’ll be baking everyone’s favorite monster cookies in a pan to create bars instead of cookies!

easy monster cookie bars

How did Monster Cookies get their name?

With a name like “Monster Cookies,” you would think that traditional Monster Cookies are humongous in size. They’re not. Monster cookies are a peanut butter oatmeal cookie baked with M&M’s and chocolate chips. The name was given to them by a Michigan photographer named Dick Wesley. Legend has it he was out of flour, so he subbed oats and added a bunch of eggs, chocolate chips and M&M candies, resulting in a very large amount of dough. He named his new creation: Monster Cookies.

two bowls - ingredients in one and dough in the other for monster cookie bars

How to make Easy Monster Cookie Bars:

Print out the complete recipe for these bars at the end of this post. The recipe will have amounts for all ingredients, as well as detailed instructions.

The wet mixture for these bars is a combination of peanut butter, butter, brown sugar, white sugar, 2 eggs, 1 egg yolk and vanilla extract.

The dry ingredients are a mix of oats, flour (yes, this version has some flour), baking soda and salt. The wet and dry ingredients are combined, and then chocolate chips and M&M’s are stirred in.

easy monster cookie bars in pan just out of oven

The dough is spread into a 9-inch square pan, and a few more M&M’s are sprinkled on top. These Easy Monster Cookie Bars bake for about 30 minutes. They’ll be golden and slightly puffy.

spatula taking out monster cookie bar out of pan

Cool for a bit before cutting. I think the edge pieces are the best ones. You get a crusty, crunchy edge along with a more tender cookie toward the middle.

easy monster cookie bars cut into pieces

If you prefer a softer bar cookie, then you’ll want to grab one of the four inside pieces! In my book, they’re all good. There will be plenty of M&M’s and chocolate chips throughout all of the cookies. If you love a good peanut butter and oatmeal cookie, then you’re going to love these Easy Monster Cookie Bars. They’re like getting a bunch of treats all-in-one dessert! Bake them today, and you’ll be so glad you did!

tray of easy monster cookie bars

Do Monster Cookie Bars freeze well?

Yes!  This recipe only makes 16 bars, but if that’s too many for you then feel free to freeze them for munching later. Layer them in a freezer zip baggie or sealed container, and freeze for up to 6 months. 

stack of 4 easy monster cookie bars

If you’re a big fan of Monster Cookies, then you must try my Christmas Monster Cookies or these Monster Cookie Chocolate Cheesecake Bars. And if you love M&M’s as much as we do, then you must try our friend Jenny’s Perfect M&M Cookies.

monster cookie bars

Easy Monster Cookie Bars
Everyone's favorite cookie baked into bars instead!
Prep Time 15 minutes
Cook Time 30 minutes
Total Time 45 minutes
Course Dessert
Cuisine American
Servings 16 bars (1 per serving)
Calories 359 kcal



  • Preheat the oven to 350℉. Generously grease a 9x9-inch pan with nonstick spray.
  • Use a handheld electric mixer to cream together peanut butter and butter in a large bowl. Beat in the brown sugar, granulated sugar, eggs, egg yolk, and vanilla extract.
  • Add the oats, flour, baking soda, and salt, and stir to combine. Stir in the chocolate chips and M&M's candy.
  • Transfer the dough to the prepared pan and spread it out evenly. Sprinkle a few more M&M’s on top.
  • Bake until the bars are golden, puffed and set- about 30 minutes. They will be more set on the outside than the inside, and will set more as they cool. Like brownies, be careful not to over-bake.
  • Cool slightly before cutting and serving.


Serving: 1barCalories: 359kcalCarbohydrates: 42gProtein: 7gFat: 19gSaturated Fat: 8gPolyunsaturated Fat: 3gMonounsaturated Fat: 7gTrans Fat: 0.3gCholesterol: 51mgSodium: 196mgPotassium: 189mgFiber: 2gSugar: 28gVitamin A: 244IUVitamin C: 0.04mgCalcium: 42mgIron: 2mg
Keyword cookie bars, cookies, monster
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