Monster Cookie Bars

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Monster Cookie Bars are filled with old fashioned oatmeal, peanut butter, chocolate chips, and mini m&ms – and make the best treats. These easy bars are quick to make and require no chill time!

Making bars are definitely no fuss. For others, be sure to take a look at my Chocolate Chip Peanut Butter Blondies, the best Frosted Sugar Cookie Bars, and some fun S’mores Cookie Bars!

Sliced monster cookie bars on a board.

M&M Cookie Bars

My mom made the best m&m monster cookies and loved making them extra large. They were impressive for sure, and I’ve given the recipe to numerous people over the years, even before I started the blog. So this recipe is just a version of those. Here’s what I did.

  • Bought a new 9×13 USA pan (linked below) and made them to fit.
  • Adjusted the monster cookie recipe because that’s a big one and I wanted them to bake well. (Not too thick and not too thin.)
  • Used mini m&ms and mini chocolate chips instead of regular sized.

Why we love these bars

  1. Simple to make. These require no chill time before baking, and you’ll need just one pan. No baking multiple batches of cookies!
  2. Delicious. Just like the cookie, these bars are tender, chewy, and full of chocolate and peanut butter. So much to love!
  3. Freeze well. You can make these ahead of time, stick them in an airtight container, and freeze for a couple of months. Be sure to use some parchment paper in between layers of bars.

NO FLOUR! This recipe does not include flour. If you want gluten-free bars, be sure to use gluten-free oats. 

A stack of three monster cookie bars on a plate.

Ingredients Used

These are classic pantry ingredients that you probably already have. You can also use substitutions, like using crunchy peanut butter instead of creamy, quick oats instead of old fashioned, and regular sized chocolate chips and M&Ms instead of mini versions.

  • Butter – I always use unsalted butter, but you could use salted if you’d like.
  • Sugars – A combo of brown sugar and granulated sugar is a perfect balance.
  • Eggs – Two large eggs required.
  • Peanut Butter – I normally use creamy peanut butter, but crunchy would also be excellent here.
  • Vanilla – I keep Watkin’s Pure Vanilla extract at the ready at all times.
  • Baking Soda – Used to leaven the bars.
  • Oatmeal – Plenty of old fashioned oatmeal gives these bars a chewy texture.
  • Chocolate Chips – Mini chocolate chips.
  • M&Ms – Mini M&Ms. Don’t forget to add a few extra to the top of the bars!

How to make Monster Cookie Bars

  1. Prep. Preheat your oven to 350 degrees. Prep a 9×13 pan with parchment paper, if desired. You can also just spray the pan with baking spray.
  2. Mix. In a large standing mixer, cream the butter and sugars together. Add the eggs, peanut butter, and vanilla, and mix again. Then add the dry ingredients – the baking soda and oatmeal – and mix again. Finally fold in the chocolate chips and m&ms by hand.
  3. Assemble. Spread the cookie mixture evenly into all sides of the pan. Press down gently to get a uniform layer.
  4. Bake. Bake for 25 minutes or so. If you want them to be more gooey, bake for less time. Let them cool for about 10 minutes if using parchment paper (and if you want to lift them out of the pan).
  5. Serve. Serve bars with a scoop of ice cream or with a tall glass of milk!
Closeup on some sliced bars.

Storing and Freezing Monster Cookie Bars

  • Storing – Place bars in an airtight container and store on the counter for three to four days.
  • Freezing – You can freeze these for up to two months. But I suggest either eating them or sharing them with neighbors and friends instead! I actually love sending goodies to Mike’s work and they get devoured quickly.

Expert Tips

  1. Be sure to use full fat regular peanut butter. Using all natural will not produce the same consistency in these and you’ll be left with a dry bar.
  2. Feel free to play around with other mix-ins. You could try different flavored chips, toffee bits, any kind of nuts, or candies.
  3. You can also use quick oats if preferred. It’s basically the same oatmeal but in smaller crumbs instead of whole oats.
  4. If you like a gooey cookie, you can decrease the cooking time. I like these browner on top, but feel free to make them the way YOU like.
Two monster cookie bars on a plate.

Kitchen Tools Used: (affiliate links)

xoxo ~Sue

Overhead shot of some monster cookie bars.

Monster Cookie Bars

Monster Cookie Bars are filled with old fashioned oatmeal, peanut butter, chocolate chips, and mini m&ms – and make the best treats. These easy bars are quick to make and require no chill time!
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Course: Dessert
Cuisine: American
Keyword: monster cookie bars
Prep Time: 15 minutes
Cook Time: 25 minutes
Total Time: 40 minutes
Servings: 16 bars
Calories: 344kcal
Author: Sue Ringsdorf

Ingredients

  • 6 Tablespoons unsalted butter – softened
  • 1 cup brown sugar
  • 1/2 cup granulated sugar
  • 2 large eggs
  • 1 cup peanut butter
  • 1 teaspoon vanilla extract
  • 1 ½ teaspoons baking soda
  • 3 ⅓ cups old fashioned oatmeal
  • ¾ cup mini chocolate chips
  • ¾ cup mini M&Ms

Instructions

  • Prep. Preheat your oven to 350 degrees. Prep a 9×13 pan with parchment paper, if desired. You can also just spray the pan with baking spray.
  • Mix. In a large standing mixer, cream the butter and sugars together. Add the eggs, peanut butter, and vanilla, and mix again. Then add the dry ingredients – the baking soda and oatmeal – and mix again. Finally fold in the chocolate chips and m&ms. I normally do this by hand.
  • Spread the cookie mixture evenly into all sides of the pan. Press down gently to get a uniform layer.
  • Bake for 25 minutes or to your liking. If you want them more gooey, bake for less time. Let them cool for about 10 minutes if using parchment paper (and if you want to lift them out of the pan).
  • Serve bars with a scoop of ice cream or with a tall glass of milk!

Notes

  • Storing – Place bars in an airtight container and store on the counter for three to four days.
  • Freezing – You can freeze these for up to two months. But I suggest either eating them or sharing them with neighbors and friends instead! I actually love sending goodies to Mike’s work and they get devoured quickly.

Nutrition

Calories: 344kcal | Carbohydrates: 41g | Protein: 7g | Fat: 18g | Saturated Fat: 7g | Polyunsaturated Fat: 3g | Monounsaturated Fat: 5g | Trans Fat: 1g | Cholesterol: 37mg | Sodium: 204mg | Potassium: 167mg | Fiber: 2g | Sugar: 33g | Vitamin A: 206IU | Vitamin C: 1mg | Calcium: 49mg | Iron: 1mg

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