Gluten Free Monster Cookie Bar Recipe

5 from 1 vote
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Crisp on the outside, chewy on the inside, these Monster Cookie Bars are fully-loaded with peanut butter, oats, chocolate chips, and M&M candies, but they have no flour. Even better, you can make this naturally gluten free flourless dessert recipe in less than 15 minutes of work and in only one bowl!

One Bowl Monster Cookie Bar Recipe image with title

Unless I am baking for the blog, finding the time to make a special treat for the family during the week in the middle of all the craziness that goes along with being a working mom of two school-age boys is next to impossible. 

Then I discovered these Monster Bars, and I have to be honest, it’s a little dangerous. Well, dangerously delicious.

You see, just like classic Monster Cookies, these bars are chock full of peanut butter, oats, chocolate chips, and M&M’s. But they come together in about 15 minutes, and you only have to dirty one bowl! And the gooey middle, peanut butter deliciousness, and chocolate overload will make everyone happy.

Whether you want a quick and easy dessert to treat the family, are looking for something to make quickly to share with friends, want to bake something simple for someone avoiding gluten, or need a recipe for leftover Halloween candy, these no flour cookie bars are perfect.

One Bowl M&M's Monster Cookie Bars cut into squares

Why This Recipe Works

Flourless Monster Cookie Bars are made with basic ingredients, many of which you already have in your pantry. They can be mixed together in one bowl in just a few minutes. There is no scooping or shaping, you just have to spread them in a single pan. And they bake up fast.

Monster Cookies are traditionally a flourless cookie, and this recipe is as well. So they are perfect to make for those that are avoiding gluten. If you are making them for someone with celiac disease or a severe gluten sensitivity, you’ll want to be sure to use cetified gluten free oats.

They are great to make ahead because they keep for several days or can be frozen.

And with all that sweet, chewy goodness, they are guaranteed to be a family favorite!

Monster Bars and Milk

Ingredients

  • Salted butter: Be sure it is softened to room temperature. If you only have unsalted butter, just add a pinch of salt to the recipe.
  • Light brown sugar: Make sure it is lightly packed.
  • White sugar: Yes, the blend of sugars makes them perfect.
  • Egg plus egg yolk: Using both adds to the chewy texture.
  • Vanilla extract: Alwayd essential in a sweet treat.
  • Maple syrup: Use the real stuff, not pancake syrup, because that pure maple flavor complements the peanut butter.
  • Baking soda: For that perfect rise, NOT baking powder.
  • Crunchy peanut butter: You can use creamy, but the chunky adds a nice texture.
  • Old-fashioned rolled oats: Not quick or instant oats. If these are being served to someone with celiac disease or a severe allergy or sensitivity, be sure to use certified gluten free rolled oats.
  • Semi-sweet chocolate chips: Milk chocolate chips can also be substituted, if you prefer.
  • M&M’s candies: This recipe calls for the classic kind, but you can use holiday ones or other flavors.

Are M&M’s gluten free?

According to the Mars website, wheat, barley, and rye ingredients by name and any wheat cross-contamination risks on the label, but may not declare possible barley or rye cross-contamination. This is recent, so if you have previously eaten M&M’s without issue, you might still want to be cautious.

But regular M&M’s and most of the standard flavors such as Peanut and Almond have no gluten ingredients. Do avoid the Pretzel and Crispy M&M’s, and use caution with special or seasonal flavors, which may be manufactured on lines where there is a risk of cross-contamination.

Scroll down to the recipe card for the full instructions, but here is a brief overview just to show you how easy this recipe is.

  1. Preheat your oven to 350°F and line your pan with parchment paper.
  2. Beat the butter and sugars in a large bowl.
  3. Blend in the egg, egg yolk, vanilla, maple syrup, and baking soda.
  4. Stir in the peanut butter, followed by the oats, and then the chocolate chips.
  5. Press the dough into the pan.
  6. Sprinkle the M&M’s on top and lightly press into the dough.
  7. Bake until lightly browned.
  8. Let cool before slicing and store in an airtight container.

No Flour Monster Cookie Squares cut on a piece of parchment paper

Yes, bar cookies are one of the ultimate make-ahead desserts. While they will stay good for several days at room temperature if you keep them tightly wrapped, they also freeze well.

Let them cool completely and cut them into bars. You can then place the bars in an airtight container. For extra protection from freezer0burn if you will be keeping them frozen for more than a month, I recommend placing the container in a freezer storage bag or wrapping it in plastic wrap. You can also wrap the bars in plastic and then place them into a freezer storage bag.

You can keep them frozen for up to two months.

Tips for Success

Some of these tips are from my experience, and some are directly from Mary, who has tested this recipe multiple times for this cookbook.

  • Line the Pan: While it says you can butter your pan well, lining the pan with parchment paper is definitely recommended. Let the parchment overhang the edges by at least an inch, then use the edges to pull the entire thing out at once. This makes it easier to slice the cooled bars on a cutting board.
  • Don’t Get Sticky: When measuring peanut butter or even something sticky like maple syrup, if you don’t have one of these incredibly useful gadgets, then grease your measuring cup with butter or cooking spray so it slides out easily.
  • Be Patient: Let them cool for at least 15 minutes. There will be some carryover cooking, they will be easier to cut, and you definitely want to store fully cooled bars.
  • Gluten Free Note: These are perfect because they are flourless, but if you are dealing with celiac or an allergy, make sure your oats are certified gluten free.
  • Get Creative: Once you have mastered the basic version, try switching it up with different nut butters and candy mix-ins. I might try almond butter and toffee!
Best Monster Cookie Bars topped with M&Ms on a plate

The Weeknight Dessert Cookbook

This recipe is from The Weeknight Dessert Cookbook by Mary Younkin of the popular food blog Barefeet in the Kitchen. She has created 80 tried and tested surefire recipes that require only 5 to 15 minutes of prep time. Sure, some might require some time in the oven, fridge, freezer, or ice cream machine. But after that short timeframe of assembling and combining the ingredients, your work is done.

The Weeknight Dessert Cookbook with recipe for Monster Cookie Bars
Two Monster Cookie Bars Recipe from The Weeknight Dessert Cookbook

What do I love about this cookbook? I’m already a fan of Mary’s recipes, both from her blog and her cookbooks. Her Barbecue Chicken Tostadas from The Weeknight Dinner Cookbook are on regular rotation in my house. And while we aren’t eggs for breakfast people, we love the Breakfast Tostadas from The Weekday Lunches and Breakfasts Cookbook. So I knew that The Weeknight Dessert Cookbook would be amazing too!

And in this book, you’ll find all of her tips and tricks for being ready to make a dessert quickly on a moment’s notice, plus recipes for everything from cakes and cookies and cobbler and crisps to bars and ice cream and no-bake treats. Plus so much more.

Even though this is not a gluten free dessert cookbook, there are still a number of naturally gluten free recipes, like these gluten free Monster Cookie Bars, as well as flourless Mexican Chocolate Lava Cakes. There is an entire chapter of ice cream, puddings, and sauces that don’t contain gluten ingredients. And most of the no-bake desserts can be made gluten free by using a few simple swaps, like gluten free chocolate sandwich cookies or pretzels.

A stack of two No Flour Monster Cookie Bars on a small white plate

Things You’ll Need

Brianne Recommends
  • These Monster Bars are made in an 8-inch square baking pan.
  • Parchment paper to line the pan makes it easier to remove the bars
  • Remember, one beauty of this recipe is that you only need one bowl
  • You can mix these bars by hand, but a hand mixer will make it easier to blend the butter and sugars together.
A stack of two No Flour Monster Cookie Bars on a small white plate
5 from 1 vote

Monster Cookie Bars

A fully-loaded bar cookie you can make in one bowl in no time. Crisp on the outside, chewy on the inside, and filled with peanut butter, oats, chocolate chips, and M&M's.
Prep: 15 mins
Cook: 16 mins
Servings: 9 bars

Ingredients

  • 3 Tablespoons salted butter, softened
  • 3/4 cup light brown sugar
  • 1/3 cup white sugar
  • 1 egg
  • 1 egg yolk
  • 1 teaspoon vanilla extract
  • 1 Tablespoon maple syrup
  • 1/2 teaspoon baking soda
  • 2/3 cup crunchy peanut butter
  • 2 cups old-fashioned rolled oats, certified gluten free if needed
  • 1/3-1/2 cup semi-sweet chocolate chips
  • 1/4-1/2 cup M&M's candies for topping

Instructions

  • Preheat the oven to 350°F. Line an 8-inch square pan with parchment paper or grease well with butter.
  • Combine the butter, brown sugar, and white sugar in a large bowl and beat to combine. Add the egg, egg yolk, vanilla, syrup, and baking soda. Stir in the peanut butter. Add the oats and stir until well combined. Mix in the chocolate chips.
  • Press the dough into the bottom of the prepared pan. Top with the M&M's and lightly press them into the dough. Bake 16 to 17 minutes, or until the bars are lightly browned and just past looking wet on top. They will not be firm, but they will set up as they cool. Let it cool completely before slicing. Store in an airtight container.

Notes

  • While it says you can butter your pan well, lining the pan with parchment paper is definitely recommended. Let the parchment overhang the edges by at least an inch, then use the edges to pull the entire thing out at once. This makes it easier to slice the cooled bars on a cutting board.
  • The recipe calls for salted butter. If you only have unsalted butter, just add a pinch of salt.
  • When measuring peanut butter, grease your measuring cup with butter or cooking spray so it slides out easily.
  • Let them cool for at least 15 minutes. There will be some carryover cooking, they will be easier to cut, and you definitely want to store fully cooled bars.
  • Baking for someone avoiding gluten? These are perfect because they are flourless, but if you are dealing with celiac or an allergy, make sure your oats are certified gluten free.
  • Once you have mastered the basic version, try switching it up with different nut butters and candy mix-ins.
Nutrition Facts
Monster Cookie Bars
Amount Per Serving (1 bar)
Calories 449.01 Calories from Fat 199
% Daily Value*
Fat 22.11g34%
Saturated Fat 8.82g44%
Cholesterol 52.25mg17%
Sodium 205.13mg9%
Potassium 282.02mg8%
Carbohydrates 56.12g19%
Fiber 4.08g16%
Sugar 39.44g44%
Protein 9.32g19%
Vitamin A 197.74IU4%
Calcium 61.26mg6%
Iron 2.17mg12%
* Percent Daily Values are based on a 2000 calorie diet.
4 Comments
  1. Mary

    5 stars
    I am so happy that you’re enjoying the cookbooks! These bars look fantastic and now I want to make them again. We love them too!

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