Monster Cookie Bars

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These Monster Cookie Bars are an easy cookie bar recipe based on the classic, beloved Gluten Free Monster Cookies! Loaded with oats, M&Ms, and chocolate chips these sturdy Monster Cookie Bars are perfect for packed lunches, afternoon snacks, and Christmas cookie gifting. Oh, and they’re gluten free too! Wahoo!

Sliced Monster Cookie Bars beside cups of milk

Growing up, my family almost always ended our dinner with dessert. It wasn’t anything fancy–often just a chocolate chip cookie or slice of warm Crazy Cake with milk on top–but all of us enjoyed ending our days on the sweet side.

I didn’t realize this was unusual until I met my husband, whose family was not accustomed to having dessert on a random Tuesday night. It was one of those small, silly differences you discover when you merge two families together, although I’m happy to say we didn’t waste any time arguing over this one.

My husband quickly got used to the ever-present Tupperware container of cookies on the counter, and we’ve been living in after-dinner-dessert bliss ever since.

Slices of Monster Cookie Bars arranged on a dark background

Cookie Bars for Dessert!

It’s this piece of my upbringing that made me so thrilled to receive Mary Younkin’s new cookbook, The Weeknight Dessert Cookbook. I’ve been following Mary’s blog, Barefeet in the Kitchen, for years and have always appreciated her easy and family friendly recipes.

Her newest cookbook is filled with 80 tried and true dessert recipes that only require 5 to 15 minutes of prep work, meaning you can enjoy them for the holidays or whip them up on a Thursday after work.

These are the types of desserts I grew up with: simple, comforting fare like zucchini sheet cake, browniesapple and blueberry crumble, with a special occasion chocolate bundt cake thrown into the mix for the holidays. There’s nothing fussy here, no fancy ingredients to hunt down or special techniques to master. Just delicious sweets anyone can make and share with their families.

I’ve long been a fan of Monster Cookies–the thick, chewy, peanut buttery concoctions packed with oats and M&Ms–so when I saw Mary had taken this classic and turned them into a quick and easy cookie bar, I was sold. I knew these Monster Cookie Bars needed to be added to our rotation.

the weeknight dessert cookbook

How to Make Monster Cookie Bars

Like the other recipes in The Weeknight Dessert Cookbook, this one is a breeze to make. It’s all made in a single bowl, meaning you can have this treat in and out of your oven in about 30 minutes.

  1. To make the bars, combine butter, brown sugar, and granulated sugar in a bowl and beat to combine.
  2. Add in an egg, egg yolk, vanilla, maple syrup, baking soda, and salt.
  3. Stir in the peanut butter followed by rolled oats. Mix in the semi-sweet chocolate chips.
  4. Spread the mixture into a greased 9 x 9 inch pan and dot with M&Ms. Bake in a 350 degree oven for 16-17 minutes and voila! You’ve got dessert!

Monster Cookie Bars: A Hit For Any Occasion

The only change I made from Mary’s Monster Cooke Bar recipe was substituting creamy peanut butter for crunchy. It’s just a personal preference, and it makes it easier for me to share this recipe with my youngest kiddo.

The resulting cookie bars are perfect for the chocolate and peanut butter lovers in your life, but even if you’re not one (I fall into this camp), I think you’ll enjoy these! Monster Cookie Bars are thick and hearty, with a layer of smooth, melty chocolate and crisp, crackly M&Ms. What’s not to love?

My son loves anything with M&Ms, so these were obviously a hit with him. I also love that they’re a bit heartier than traditional cookies (thanks oats!), so they fill him up longer. This is one of our favorite after preschool snacks, especially alongside a glass of cold milk.

Want to include Monster Cookie Bars on your holiday cookie trays? Simply replace the standard M&Ms with the red and green variety for some festive color!

Monster Cookie Bars with M&Ms on a dark background

How do you know when monster cookie bars are done?

These bars will puff up while they’re in the oven and develop a golden color. Take them out when the middle no longer looks wet, or use the toothpick test. Insert a toothpick into the center of the pan, and if it comes out clean (or just with some melty chocolate), it’s done!

How long do cookie bars keep?

Monster Cookie Bars keep incredibly well, and are a great sturdy cookie to pack in school lunches. You can keep them in an airtight container at room temperature for 5-7 days or wrap individual slices in saran wrap.

Can you freeze cookie bars?

Bar cookies typically freeze beautifully, and Monster Cookie Bars are no different! You can either freeze the entire slab or individual slices of cookie. Wrap the slab or individual slices in a double layer of saran wrap followed by foil. Freeze for up to 3 months. Thaw at room temperature for several hours.

For more information, visit my post all about freezing cookies.

Monster Cookie Bar square dotted with M&Ms

More Recipes for Peanut Butter Lovers

If you love a peanut butter dessert, you have to give these classic Soft and Chewy Peanut Butter Cookies a try.

If you like your peanut butter to be paired with chocolate, try these ultra rich Buckeye Brownies or my husband’s favorite Reese’s Peanut Butter Cookies.

More Brownies and Bar Cookie Recipes!

Looking for more easy bar cookies? These are a few of my favorites:

7 Layer Bars– Chocolate and coconut and cashews, OH MY!

Brown Butter Pecan Blondies– So rich and butterscotchy.

No Bake Peanut Butter Bars– For the chocolate and peanut butter purists.

One Bowl Fudgy Chocolate Brownies– Classic, better than the box brownies

Old World Raspberry Bars– Simple, summery, with bright fruit flavor, these are one of my absolute favorites.

Monster Cookie Bar square dotted with M&Ms

Monster Cookie Bars

Monster Cookie Bars combine oats, peanut butter, chocolate, and M&Ms for a chewy and hearty cookie the whole family will love.
5 from 9 votes
Print Pin
Prep Time: 10 minutes
Cook Time: 16 minutes
Total Time: 26 minutes
Servings: 12
Calories: 338kcal


  • 3 Tablespoons unsalted butter (softened)
  • 3/4 cup light brown sugar
  • 1/3 cup granulated sugar
  • 1 egg
  • 1 egg yolk
  • 1 teaspoon vanilla extract
  • 1 Tablespoon maple syrup
  • 1/2 teaspoon baking soda
  • 1/4 teaspoon salt
  • 2/3 cup creamy peanut butter
  • 2 cups old fashioned rolled oats (certified GF if needed)
  • 1/2 cup semi sweet chocolate chips
  • 1/2 cup M&M candy


  • Preheat the oven to 350 degrees. Grease an 8 inch square pan with butter, or, if you'd like to be able to remove the entire slab of cookies, grease and line with parchment paper, allowing it to go several inches up the sides to create a "sling."
  • Combine the butter, brown sugar, and white sugar in a bowl. Beat together until smooth. Add the egg, egg yolk, vanilla, syrup, baking soda, and salt, beating until combined.
  • Stir in the peanut butter followed by the oats. Stir in the chocolate chips.
  • Spread the dough into the prepared pan. Dot with M&Ms, pressing them gently into the dough.
  • Bake for 16-17 minutes or until the top is light browned, but not completely set. Let the bars set up and cool completely before slicing.


  • Store in an airtight container or freeze for up to 3 months.
Course Cookies
Cuisine American
Keyword cookie bars recipe, easy cookie bars, monster bars, monster cookie bars


Calories: 338kcal | Carbohydrates: 42g | Protein: 7g | Fat: 17g | Saturated Fat: 7g | Polyunsaturated Fat: 2g | Monounsaturated Fat: 6g | Trans Fat: 0.1g | Cholesterol: 39mg | Sodium: 173mg | Potassium: 202mg | Fiber: 3g | Sugar: 30g | Vitamin A: 152IU | Vitamin C: 0.1mg | Calcium: 47mg | Iron: 2mg
Did You Make This Recipe?Leave a review, Mention @NeighborFoodie, or tag #neighborfoodies!

One Comment

5 from 9 votes (9 ratings without comment)

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