This post may contain affiliate links.

With a buttery oatmeal crumble, a soft & creamy peanut buttery filling and plenty of M&M’s, these Monster Cookie Bars will be gone in an instant!

Jump to Recipe
Two monster cookie bars with a glass of milk in the background.

Traditional monster cookies combine M&M’s with chocolate chips, peanut butter and oatmeal….all that goodness packed into one glorious cookie.  I’m pretty sure they named them “monster” cookie, because the bigger the better, right?!

These chewy Monster Cookie Bars are extra delicious, thanks to the ribbon of smooth peanut buttery filling!

The ingredients needed to make chewy Monster Cookie Bars on a white background.

Ingredients Needed (Amounts in Recipe Card Below)

  • Oats – I prefer the texture of quick oats over old-fashioned oats (aka rolled oats), but you can use either.
  • All Purpose Flour 
  • Brown Sugar – I prefer brown sugar over white sugar in these; the molasses in brown sugar helps keep them soft and chewy!
  • Baking Soda 
  • Salt 
  • Butter – I use salted butter.
  • Creamy Peanut Butter – For best results, I do NOT recommend using natural peanut butter as the texture is unpredictable.
  • Egg – I always use large eggs when baking.
  • M&M Candies – Regular or mini M&M candies are great!  If you want to boost the peanut butter flavor even more, try using Reese’s Pieces instead!  (Perfect for leftover Halloween candy!)
  • Chocolate Chips – I like to use semi-sweet or dark chocolate chips to balance out the sweetness of the filling.  However, you could use a combination of chocolate chips, peanut butter chips and/or white chocolate chips if you prefer!
  • Sweetened Condensed Milk – Do not confuse this with evaporated milk! (Very different texture!)

How to Make Monster Cookie Bars

Start by preheating your oven and lining a 9×13-inch pan with parchment paper or greasing with cooking spray.

Then, combine the dry ingredients (oats, flour, brown sugar, soda and salt) in a large bowl or in the bowl of a stand mixer.  

Then add the melted butter, peanut butter and egg; stir until well-combined then mix in the candies and chocolate chips.

Monster cookie dough pressed into a parchment paper lined baking pan.

Press a little over half of the mixture into the prepared baking pan and set aside.

In a separate bowl, stir together the filling ingredients.  Pour over the bottom oatmeal layer and spread to a smooth layer.

Monster Cookie Bars ready to go into the oven.

Sprinkle the remaining dough on top and press into the filling a bit.

Bake until golden brown around the edges.  The baking time will vary with different ovens and baking pans, so I recommend starting with less baking time and adding more if needed.  It’s SO important that you do NOT over-bake these chewy bars!

Two cookie bars stacked up on a white piece of parchment paper with m&m candies around it.

​Make them Festive!!

One reason I love these bars is because I can make them festive for almost any holiday using different colorful M&M candies (just like in my M&M Cookie Bars!).  They’re a huge hit no matter what time of year it is!

Two monster cookie bars stacked up with a scoop of vanilla ice cream on top and a drizzle of hot fudge.

Try these warm with a scoop of vanilla ice cream – highly recommended!!!

Can I Make these Monster Bars Gluten Free?

Yes!!!  You’ll need to switch out the wheat flour for an all purpose 1-to-1 gluten free flour.  Also, if you’re planning to serve these to someone with celiac disease, you’ll want to make sure the oats are certified gluten free and the peanut butter is free of bread crumbs! 🙂

How do you Store Monster Cookie Bars?

I recommend letting them cool on the counter before cutting. Cover them with plastic wrap or store them in an airtight container at room temperature for up to 5 days.  You can also freeze these for up to 2 months.

A hand holding a M&M oatmeal cookie bar.

Other Delicious Cookie Bars

Two monster cookie bars with a glass of milk in the background.
5 from 1 vote

Monster Cookie Bars

Author: Kelsey
Prep Time 15 minutes
Cook Time 20 minutes
Cool Time 30 minutes
Total Time 1 hour 5 minutes
With a buttery oatmeal crumble, a soft & creamy peanut buttery filling and plenty of M&M's, these bars will be gone in an instant!


  • One 9×13-inch pan


Monster Cookie Dough

  • 2 1/2 cups quick oats
  • 1 1/2 cups flour
  • 1 cup brown sugar
  • 1 teaspoon baking soda
  • 1/2 teaspoon salt
  • 1 cup melted butter
  • 1/3 cup creamy peanut butter
  • 1 egg
  • 1 cup M&M candies mini or regular sized
  • 1 cup semi-sweet chocolate chips

Peanut Butter Filling

  • One 14 ounce can sweetened condensed milk
  • 1/3 cup creamy peanut butter


  • Preheat oven to 350 and grease a 9×13-inch pan with cooking spray or line with parchment paper.
  • Combine the oats, flour, brown sugar, soda, and salt and mix well.
    2 1/2 cups quick oats, 1 1/2 cups flour, 1 cup brown sugar, 1 teaspoon baking soda, 1/2 teaspoon salt
  • Stir in the melted butter, peanut butter and egg.
    1 cup melted butter, 1/3 cup creamy peanut butter, 1 egg
  • Stir in the chocolate chips and M&M's.
    1 cup M&M candies, 1 cup semi-sweet chocolate chips
  • Press all but 1 1/2 cups of the oatmeal mixture into a greased 9×13 pan. (Set the 1 1/2 cups aside for later.)
  • Stir together the sweetened condensed milk and peanut butter and drizzle over the bottom crust. Spread gently to evenly coat.
    One 14 ounce can sweetened condensed milk, 1/3 cup creamy peanut butter
  • Sprinkle the remaining oatmeal mixture on top and lightly press down.
  • Bake 20-25 minutes or until a light golden brown. The middle should be slightly wiggly! It will firm up as the bars cool. It's super important that you DO NOT over-bake these! 🙂
  • Let the bars cool for 30 minutes before cutting into squares.


Calories: 310kcal | Carbohydrates: 39g | Protein: 5.4g | Fat: 16.1g | Saturated Fat: 8.7g | Polyunsaturated Fat: 0.9g | Monounsaturated Fat: 4.8g | Cholesterol: 35.4mg | Sodium: 129mg | Potassium: 170mg | Fiber: 1.7g | Sugar: 26g | Vitamin A: 85IU | Vitamin C: 0.4mg | Calcium: 65mg | Iron: 0.9mg
“Dance Around the Kitchen” is not a dietitian or nutritionist, and any nutritional information shared is an estimate. If calorie count and other nutritional values are important to you, we recommend running the ingredients through whichever online nutritional calculator you prefer. Calories and other nutritional values can vary quite a bit depending on which brands were used.

did you love this recipe?

Share it with me on Facebook and find more recipes on Pinterest for more!

Leave a Reply

Your email address will not be published. Required fields are marked *

Recipe Rating

One Comment

  1. 5 stars
    Definitely the best Monster Cookie Bar recipe I have ever made!! Definitely a keeper 🙂 Thank you for sharing as it will be a go-to recipe for me!