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Monster Cookie Bars

Monster Cookie Bars

These monster cookie bars are super easy to make and loaded with peanut butter, oats, chocolate chips, and M&M’s. The kids will love them!

Monster cookies are one of the best cookies around. Peanut butter, oatmeal, chocolate chips, and M&M’s all in one cookie – it doesn’t get much better.

monster cookie bars

Except maybe as a cookie bar. Mostly because they’re even easier to make in cookie bar form. Instead of scooping individual cookies, you toss all the dough in a pan and bake it up.

They’re so easy to make, and so tasty. Filled with peanut butter, oats, and chocolate, they make an absolutely delicious cookie bar that everyone will love!

easy monster cookie bars

What are monster cookie bars made of?

Monster cookie bars are filled with peanut butter, oats, chocolate chips, and M&M’s. They’re chewy, hearty, and delicious cookie bars filled with all sorts of good things!

They’re quite adaptable too. If you want different or additional mix-ins, you can easily change it up.

There’s two cups total of chocolate chips and M&M’s in this recipe, but you can change that to any combination you’d like. They would also be great with peanut butter chips, dark chocolate chips, chopped pretzels, mini peanut butter cups – so many options!

monster cookie bars

Which type of pan is used for baking bar cookies?

Typically you use a metal pan for baking bar cookies. The metal heats up faster and bakes the cookie dough more evenly than a glass pan will.

I always use a metal pan for these monster cookie bars, so the baking time is based on that. If all you have is a glass pan, I would recommend lowering the oven temperature to 325F, and you will likely need to bake the bars for an extra 5-10 minutes.

chewy monster cookie bars

Can you use quick oats in monster cookies?

For these monster cookie bars I prefer to use quick oats instead of old fashioned rolled oats, so the recipe is written that way. For my Monster Cookies recipe I prefer to use old fashioned rolled oats, as they give the cookies a chewier texture.

But for these cookie bars, I found that old fashioned rolled oats resulted in a crumblier texture. I’ve made them with both though, and both were delicious, so use your preference.

easy monster cookie bars

How to make Monster Cookie Bars:

  • Make sure not to over-bake these cookie bars or they will end up a bit crumbly and less chewy.
  • The dough will be very soft and sticky, don’t worry about it, it will bake up fine, just spread it in a baking pan as evenly as possible.
  • The recipe is written with quick oats, as that was my preference, but I’ve made these with old fashioned rolled oats as well and they are great too, just a bit crumblier in texture.
  • If you want to change up the mix-ins, that’s totally fine. Lots of different combinations would be delicious in these cookie bars.
monster cookie bars

Here are some more great cookie bar recipes for you:

monster cookie bars
Yield: 24 bars

Monster Cookie Bars

easy monster cookie bars

These monster cookie bars are super easy to make and loaded with peanut butter, oats, chocolate chips, and M&M's. The kids will love them!

Prep Time 20 minutes
Cook Time 25 minutes
Total Time 45 minutes


  • 3/4 cup unsalted butter, softened
  • 1/2 cup granulated sugar
  • 1 1/2 cups brown sugar, lightly packed
  • 2 large eggs
  • 1 1/4 cup peanut butter
  • 2 teaspoons vanilla extract
  • 1 1/2 cups all purpose flour
  • 2 1/2 cups quick oats
  • 1 teaspoon salt
  • 1 teaspoon baking soda
  • 1 cup semi-sweet chocolate chips
  • 1 cup M&M’s candy


  1. Preheat the oven to 350 degrees F.
  2. Line a 9x13” baking pan with foil or parchment paper, leaving an overhang, and lightly spray it with non-stick cooking spray. Alternatively you can just spray the pan and skip the liner, it just makes for easier slicing as you can lift the bars out of the pan.
  3. In a stand mixer with the paddle attachment, or in a large bowl with an electric mixer, cream the butter, sugar, and brown sugar together until light and fluffy.
  4. Add the eggs, peanut butter, and vanilla, and mix until smooth and well combined.
  5. Add the flour, quick oats, salt, and baking soda, and mix again until well combined. 
  6. Mix in the chocolate chips and M&M’s.
  7. Press the dough evenly into the prepared baking pan (it will be quite soft). 
  8. Sprinkle a few more chocolate chips and M&M’s on top if desired.
  9. Bake the cookie bars for 22-27 minutes, or until they are golden brown on top. Try not to over-bake them or they may be crumbly.
  10. Let the bars cool completely in the pan, then lift them out with the foil overhang and slice them into bars. Store the bars in an airtight container at room temperature for up to 5 days, or freeze them for up to 3 months.


I use a metal baking pan for these bars. If you're using a glass pan, you may want to decrease the oven temperature to 325F, and will likely need to bake the cookie bars for an additional 5-10 minutes.

You can substitute old fashioned rolled oats for the quick oats. They are delicious either way, they just end up a bit crumblier with the rolled oats.

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Nutrition Information:



Serving Size:

1 cookie bar

Amount Per Serving: Calories: 329Total Fat: 17gSaturated Fat: 8gTrans Fat: 0gUnsaturated Fat: 8gCholesterol: 32mgSodium: 240mgCarbohydrates: 40gFiber: 2gSugar: 26gProtein: 6g

Nutrition Information is estimated based on ingredients used and may not be exact.

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