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Hi there, Yellow Bliss Road friends! It’s Samantha from Five Heart Home, where I share quick and easy, family-friendly, real food recipes…and today I’m thrilled to be guest posting for the lovely, talented Kristin! I’m equally excited about the recipe that I brought over…oat-filled, peanut butter-y, M&M studded Monster Cookie Bars. 🙂

Social media image of Monster Cookie Bars

You read that right…these little babies are positively loaded with this good stuff. But let’s back up for just a moment. You’ve all heard of Monster Cookies, right? They’re known for being nice and chewy thanks to rolled oats, they have an unmistakable (and delicious) undertone of peanut butter, and this version boasts not one, not two, but THREE different types of candy confections: M&Ms, chocolate chips, and peanut butter chips!

Well, I’m notorious for turning classic cookies into bar cookies, because when I need to bring a baked treat to an event, I’ve found that it’s way faster to spread batter in a pan and bake as opposed to hand-forming dozens of individual cookies. So I took a classic Monster Cookie Recipe and did just that…baked the batter in a 9- by 13-inch baking pan. Unfortunately, my cookies turned out pretty thick, which resulted in them being a bit too underdone in the center and a bit too overdone around the edges of the pan…not that we didn’t happily eat the rejects, mind you. 😉

Anyway, I decided to scrap that approach, tweak my ingredient amounts, and try, try again, this time taking a hint from my favorite brownie recipe and making these bars in a large, rimmed sheet pan for more even baking. And ding, ding, ding…it worked! The cookies were perfectly soft and chewy without being too gooey in the middle or too crunchy along the edges. In other words, Monster Cookie Bar perfection!

A close up of Monster Cookie Bars

And did I mention how easy they were to whip up?! This batter comes together really quickly — there’s not even any flour to measure out — and the large sheet pan makes a ton of bars, meaning this recipe is perfect when you need a large quantity of treats in one easy batch. In fact, I took a pan of Monster Cookie Bars to my high school reunion one weekend, and then following week I made them again for my 6-year-old’s class birthday treat (I should note that there are no peanut allergies in his class, so make sure that’s the case if you bake these for a group). They were a hit at both events!

A tray of Monster Cookie Bars

Finally (and then I promise to stop blabbing), I love these bar cookies because the M&Ms make them fun to customize for various holidays. You could use Reese’s Pieces in place of M&Ms for pretty fall colors, or buy seasonal M&Ms in color schemes from Halloween to Christmas to Easter to the 4th of July for festive, holiday-themed cookie munching all year long.

So the next time you need a large batch of effortless cookies for sharing, look no further than these Monster Cookie Bars! They’re colorful, they’re fun, they’re totally addictive…and I promise that your big ol’ cookie sheet will be empty in no time. 😉

A close up of Monster Cookie Bars

Social media image of Monster Cookie Bars

Monster Cookie Bars

4.50 from 8 votes
You've heard of monster cookies, but these oat-filled, peanut butter-y, M&M studded Monster Cookie Bars have them beat!
Prep Time 10 minutes
Cook Time 18 minutes
Total Time 28 minutes
Servings 24 bars


  • 4 eggs
  • 1 1/2 cups sugar
  • 1 cup brown sugar
  • 3/4 teaspoon salt
  • 1 tablespoon pure vanilla extract
  • 16 ounces peanut butter (creamy or crunchy) 2 cups
  • 5 tablespoons butter at room temperature
  • 2 1/2 teaspoons baking soda
  • 18 ounce old-fashioned oats 5 cups
  • 1 cup M&Ms
  • 1/2 cup semisweet chocolate chips
  • 1/2 cup peanut butter chips
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  • Position rack in center of oven and preheat to 350°F. Generously butter a 12x18x1-inch rimmed baking sheet. Set aside.
  • In a very large bowl (using a spoon or electric mixer), mix together the eggs and sugars until well-combined. Beat in the salt, vanilla, peanut butter, and butter until smooth. Stir in the baking soda (make sure there aren't any lumps) and the oats, then add the M&Ms, chocolate chips, and peanut butter chips and mix until just combined.
  • Spread the batter into the prepared baking pan, pressing down and smoothing the top into an even layer. Bake for 18 to 22 minutes or until edges are very light golden brown and center is set. Allow to cool in the baking pan before slicing and serving.


I love lining the pan with paper because then I can easily remove the bars to slice on a cutting board so I'm not cutting up my pan.
Keyword cookie bars, monster cookie bars, monster cookies


Calories: 394kcalCarbohydrates: 50gProtein: 9gFat: 19gSaturated Fat: 7gPolyunsaturated Fat: 3gMonounsaturated Fat: 7gTrans Fat: 1gCholesterol: 36mgSodium: 314mgPotassium: 229mgFiber: 4gSugar: 32gVitamin A: 134IUVitamin C: 1mgCalcium: 45mgIron: 2mg

Nutritional Disclaimer Kristin Maxwell of "Yellow Bliss Road" is not a dietician or nutritionist, and any nutritional information shared is an estimate. For accurate calorie counts and other nutritional values, we recommend running the ingredients through your preferred online nutritional calculator. Calories and other nutritional values can vary depending on which brands were used.

Thanks so much for having me today, Kristin and YBR readers! I hope to see you again soon over at Five Heart Home!

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You might also enjoy these delicious cookie recipes:

Chocolate Dipped Cheesecake Cookies

Chocolate Dipped Cheesecake Cookies

Caramel Stuffed Snickerdoodles

Caramel Stuffed Snickerdoodles

Orange Coconut Oatmeal Cookies

Orange Coconut Oatmeal Cookies

For all desserts go HERE and for all recipes go HERE.

Kristin Maxwell

Kristin Maxwell is the creator and main recipe developer, writer, and photographer of Yellow Bliss Road. A self-taught cook and self-appointed foodie, she specializes in easy, flavorful and approachable recipes for any home cook.

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  1. Julie Tumino says:

    This is by far my favorite recipe and my family loves them also <3

    1. Kristin says:

      Nice! Thanks for stopping by Julie.