Monster Cookie Bars

from 8 votes

Preheat your oven for the ultimate soft and chewy Monster Cookie Bars recipe made with oatmeal, chocolate chips and peanut butter.

The best monster cookie bars sliced into triangles

Monster Cookies and I go way back, like 2008 back. We’re talking the pre-Pinterest-dawn-of-hashtags days.

The best recipes stand the test of time (and technology). Monster Cookies are no exception. It’s been six years since I first hit publish on that recipe for Monster Cookies, and dozen after dozen, month after month, year after year, the cookies have popped up at birthday parties and at sports games, as an after-school snack and as a cold weather comfort. Now, they’re getting a makeover, and I don’t know who is more excited about it, me or my sous chef, Wiley.

Monster Cookie Bars Recipe

Monster Cookies, meet your culinary cousin, Monster Cookie Bars. The bars are denser, chewier and more durable for on-the-go snacking than their drop-cookie counterpart. Both desserts are flourless and both desserts contain a whole lot of peanut butter and chocolate. And because they also contain a hearty serving of oats, Monster Cookie Bars are technically a breakfast food. How convenient is that?

Monster Cookie Bars #recipe

Monster Cookie Bars #recipe

Monster Cookie Bars #recipe

Monster Cookie Bars #recipe

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Monster Cookie Bars

Soft and chewy flourless Monster Cookie Bars loaded with peanut butter, oats and chocolate.
Author: Kelly Senyei
4.38 from 8 votes
The best monster cookie bars sliced into triangles
Prep Time 15 minutes
Cook Time 35 minutes
Total Time 50 minutes
Servings 24 bars


  • 1 cup sugar
  • 1 cup brown sugar
  • 1/2 cup (1 stick) unsalted butter, at room temperature
  • 3 large eggs
  • 1 1/2 cups peanut butter (smooth or chunky)
  • 1 Tablespoon vanilla extract
  • 2 teaspoons baking soda
  • 1/2 teaspoon salt
  • 4 1/2 cups Old Fashioned oats
  • 1 cup M&Ms
  • 1 cup chocolate chips


  • Pre-heat the oven to 350°F and line a 13x9-inch metal baking pan with greased parchment paper with a 2-inch overhang on each short side of the pan.
  • In the bowl of a stand mixer fitted with the paddle attachment, cream together the sugar, brown sugar and butter until light and fluffy, about 2 minutes.
  • Add the eggs to the bowl, one at a time, beating between each addition then add the the peanut butter, vanilla extract, baking soda and salt and mix until well combined.
  • Add the oats and mix just until combined. Stir in the M&Ms and chocolate chips.
  • Transfer the cookie dough into the prepared pan, pressing it into an even layer. Bake for about 30 minutes until a toothpick inserted comes out clean. (See Kelly's Notes.) Remove the pan from the oven and allow the cookie to cool in the pan for 20 minutes. Using the parchment paper overhang, lift the cookie out of the pan and onto a cutting board. Slice the cookie into 24 bars and serve.

Kelly's Note:

  • For chewier, softer cookie bars, underbake the cookie and allow it to cool in the pan for 30 to 45 minutes before slicing and serving.
  • If you are using a glass 13x9-inch baking pan, you may need to decrease the oven temperature to 325°F based on how the heat circulates in your oven.
  • ★ Did you make this recipe? Don't forget to give it a star rating below!


Calories: 343kcal, Carbohydrates: 41g, Protein: 7g, Fat: 17g, Saturated Fat: 6g, Cholesterol: 33mg, Sodium: 236mg, Potassium: 179mg, Fiber: 2g, Sugar: 29g, Vitamin A: 185IU, Vitamin C: 0.1mg, Calcium: 45mg, Iron: 1.3mg


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Recipe by Kelly Senyei of Just a Taste. Please do not reprint this recipe without my permission. If you'd like to feature this recipe on your site, please rewrite the method of preparation and link to this post as the original source.

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  1. We LOVE these bars!! I always put them in a large 11×17 baking sheet and only bake for 15-20 minutes and they are sooo chewy and yummy! Thank you!!

  2. 5 stars
    Always get positive feedback and a request for the recipe when i bring these to a party. My family loves eating the edges and corners that I cut off before serving.

  3. 5 stars
    I used to make these all the and take them to work as a treat for my co-workers, they loved them! Since retiring, my grandkids and dil beg me to bake them. They turn out wonderfully every time!

  4. I too had problems getting these to cook all the way. 30 mins and still very wet on the inside. Going on 50 mins now and still not done. Hoping they don’t completely burn on the edges.

    1. I’m sorry you didn’t enjoy the recipe, Kristin. Ovens and baking pans can cause discrepancies in baking times however, I may need to rework this recipe.

  5. 3 stars
    I wish that I had read the comments before making these… I baked mine according to the instructions and they are doughy in the middle. However they looked done on the outside! I’d probably recommend halving the recipe like mentioned above, or spread it out on a larger sheet. It’s a bit much for a 9 x 13 pan. :(

    1. Thank you for your comment, Cassandra. I’m sorry you didn’t enjoy the recipe. Ovens and baking pans can cause discrepancies in baking times.

    1. Hi there! Every recipe on the site includes estimated nutritional info. All you have to do is click on the purple button below the recipe that says ESTIMATED NUTRITION INFORMATION.

  6. 3 stars
    My daughter made this recipe last night. The cooking time said 30 mins at 350 degrees but less for chewy bars in a 9″x13″ pan. I was concerned on cooking time with such thick bars but she followed the instructions as stated. She baked for 26 mins. They were not done. In the end she cooked for an additional 20 mins with no luck. The clean toothpick trick doesn’t work well either when you have melted chocolate that sticks to it. They smelled & looked wonderful, sides more done than center. Our oven is fairly new. She also didn’t realize to save more M&M’s back for the top decorations. She felt it was a waste of her time & money since it is costly to make. Not a good choice to make for an inexperienced baker.

    1. Hi there! I’m sorry you didn’t enjoy the recipe. Ovens and baking pans can causes discrepancies in baking times.

  7. I make the full recipe but bake it in my Pampered Chef rectangle cookie sheet. The are the right thickness. I set the time for 20 minutes and go from there as to how long I bake it. My grandkids ask for these any time they need cookies for something.

  8. For anybody who doesn’t maybe want them quite as thick (they bake up to pretty much fill the depth of the 9X13), I tested this out the second time I baked these… Make half the recipe (the only thing that doesn’t halve easily is the eggs–I just put in 2 eggs) and still put it in the 9X13. I baked mine for 20 minutes then, and they were perfect! Still get to experience the deliciousness of this recipe but in a thickness more common to most cookie bars. We love them!
    Kelly, this really is an amazing recipe! Thanks so much for sharing it!

    1. Hi there, Nita! That should work, although it may alter the texture. I would add it at the same time you add the oats. Let me know how it turns out if you give it a shot!

    1. Hi Nyda! You can use another type of nut butter, such as almond butter, however the texture might be slightly different.

  9. Can I use quick oats instead of old fashioned cause that’s all I have and I have a bunch of it? Also if I use a jelly roll pan will they come out chewy still ?

  10. Hi Kelly, these are definitely my new go to recipe also. I don’t even need the recipe’s “all in the vault”. It’s so much nicer making bars as opposed to cookies, whole lotta wasted space between those cookies don’tcha know. I made the original a few times…AWESOME!! Then I added a tbs of cinnamon…also delish! I also subbed granola for the oats..also delish…But..the coo de however you spell it, was subbing Cinnamon Toast Crunch for the oats…seriously The BOMB!! Try it sometime and Thanks for all the great recipes. =) Hargo

    1. Love all of these twists on the recipe, Hargo! Thanks for sharing and so glad you’re enjoying the recipe :)

  11. I put my cookie bars in the oven for 40 minutes but when i stick a toothpick in it still comes out unclean. What should I do?

  12. Hi Kelly! That was really cool! Can’t wait for making this cake. Thanks for the recipe!
    I want to ask you something,what is the size of cup that you use ?
    And the oatmeal, can i use with a different brand?

  13. Kelly! I have had such good luck with your recipes, so I was so excited to try this one tonight. I can’t figure out what happened, but I know I used the exact ingredients listed (Jif PB) and used a 10×15 Pyrex pan to make them thinner, and after 25 minutes the tester looked clean, but after sitting for 20 minutes they were practically goo in the middle. I put them in the oven again for 25 for minutes and they still don’t look done. Any ideas? They smell delicious, at least. :)

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