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With or without ice cream and hot fudge, these Monster Cookie Bars are sure to be a hit! Peanut butter, M&Ms, oatmeal…they’re the trifecta of perfect cookie bar. These are better than pioneer woman and taste of home combined!

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stack of monster cookie bars
Table of Contents
  1. What are Monster Cookie Bars?
  2. Ingredients in my Monster Bar Recipe
  3. How to make Monster Cookie Bars
  4. Variations and Expert Tips
  5. Monster Cookie Bars FAQ
  6. Other Favorite Recipes
  7. Monster Cookie Bars Recipe

Have you ever had a monster cookie? It’s a peanut butter oatmeal cookie that’s filled with chocolate chips and M&Ms. I love them, because they’re a combination of two of my favorite cookie recipes. But as much as I like cookies, I think I like cookie bars better because there is no scooping. I just press the dough in the pan and bake it, easy peasy.

This recipe starts with my favorite peanut butter cookie recipe. I adapted it to add oats to make it MONSTER. And, of course, I added chocolate chips, regular M&Ms, and PEANUT BUTTER M&M’s. I swear, peanut butter M&M’s are my downfall. I can easily eat a 1 lb. bag all by myself!

Once you bake them they become a soft and gooey cookie bar that’s perfect for when you’re craving peanut butter and oatmeal cookies together.

stack of cookie bars on white plate with M&Ms and Ala mode

Ingredients in my Monster Bar Recipe

Butter: As always, I start with unsalted butter that’s been softened. Learn to soften butter quickly!

Peanut Butter: A must for monster cookies! You can use creamy or crunchy, but use a no-stir brand.

Sugar: Both granulated and brown sugar makes a soft and chewy bar.

Eggs: Be sure to buy large eggs.

Vanilla: For flavor

Salt: Needed when starting with unsalted butter!

Flour: I always use all-purpose flour, be sure to measure it correctly.

Quick Cooking Oats: I prefer baking with quick oats. To make these bars with old fashioned oats you just need to pulse the oats in a food processor to break them down – learn to make your own quick oats!

Mix-Ins: Chocolate Chips and M&Ms

  1. Preheat oven to 350°F. Line a 9×13” pan with foil and spray with nonstick cooking spray.
  2. Beat butter and peanut butter with a hand or a stand mixer until smooth. Mix in both sugars until creamy. Add eggs, vanilla, baking soda, and salt and mix until smooth, then slowly mix in the flour and oats. Stir in the chocolate chips and M&Ms.
  3. Press cookie dough into the prepared pan. If desired, sprinkle more M&Ms on top for decoration. Bake for 22-25 minutes or just until the edges are golden brown.
stack of cookie bars

Variations and Expert Tips

  • Make Christmas Monster Cookie Bars with holiday M&Ms
  • Reese’s Pieces Monster Cookie Bars would be fantastic – just swap the M&Ms for Reese’s Pieces!
  • Do not over bake these – they’re best a little under baked and gooey
  • How to serve Monster Bars: I love serving these plain, just as a bar cookie, or topping with ice cream!
How long to bake monster cookie bars?

Bake these 22-25 minutes or until they just lose their glossy sheen.

How to store cookie bars? Can you freeze monster cookie bars?

Store these in an airtight container. Freeze for up to 3 months.

Can you make monster cookie bars into cookies?

It’s not an exact swap so I suggest making gluten free monster cookies instead.

Other Favorite Recipes

Have you made this recipe?

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stack of monster cookie bars
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Monster Cookie Bars – this easy bar cookie recipe is full of peanut butter, oats, and tons of M&Ms! EVERYONE loves these, especially with ice cream!
Prep Time 15 minutes
Cook Time 30 minutes
Total Time 45 minutes
Yield 24 bars
Serving Size 1 bar


  • ½ cup (113 g) unsalted butter softened
  • 1 cup (268 g) peanut butter
  • ¾ cup (150g) packed brown sugar
  • ½ cup (100g) granulated sugar
  • 2 large eggs
  • 1 teaspoon vanilla extract
  • ½ teaspoon baking soda
  • ½ teaspoon salt
  • ¾ cup (93g) all-purpose flour
  • 3 cups (256g) quick cooking oats
  • 1 cup (170g) chocolate chips
  • 2 cups M&Ms any kind, I used regular and peanut butter


  • Preheat oven to 350°F. Line a 9×13” pan with foil and spray with nonstick cooking spray.
  • Beat butter and peanut butter with a hand or a stand mixer until smooth. Mix in both sugars until creamy. Add eggs, vanilla, baking soda, and salt and mix until smooth, then slowly mix in the flour and oats. Stir in the chocolate chips and M&Ms.
  • Press cookie dough into the prepared pan. If desired, sprinkle more M&Ms on top for decoration. Bake for 22-25 minutes or just until the edges are golden brown. Cool before cutting into bars.
  • These are great served as bars or as an ice cream sundae! Store in an airtight container for up to 3 days or freeze for up to one month.

Recipe Video

Recipe Nutrition

Serving: 1bar | Calories: 322kcal | Carbohydrates: 40g | Protein: 6g | Fat: 16g | Saturated Fat: 7g | Polyunsaturated Fat: 2g | Monounsaturated Fat: 4g | Trans Fat: 1g | Cholesterol: 28mg | Sodium: 146mg | Potassium: 126mg | Fiber: 2g | Sugar: 28g | Vitamin A: 194IU | Vitamin C: 1mg | Calcium: 48mg | Iron: 1mg
Nutritional information not guaranteed to be accurate
Course Dessert
Cuisine American
Author Dorothy Kern
Keyword cookie bar

Click here to see more PEANUT BUTTER recipes! 

When I used to write stories:

When I was in the throes of toddlerhood, I would never have guessed the challenges of parenting an older kid. Jordan is now 11 (and a half!) and she’s in that weird in-between stage between needy kid and more self-sufficient teenager. She’s also the first (and only) child, so I’ve never crossed any of these parenting situations before. It’s all new to me, which makes me a tad more overprotective and worried than, say, someone whose done it all a few times.

Pretty much daily these days I’m faced with scary decisions: can she stay in the car while I run into Starbucks? Can she stay home alone? Can she walk the dog alone? Is it okay to let her run into the grocery store by herself to buy gum? Every time a situation pops up my stomach clenches in fear and indecision: what do I do?

Last week Mel was out of town so we went to my parent’s house for a few days. It’s a 2-hour drive and neither of us can make it without stopping. We had the dog with us, and it was 105°. For days before we left, the question played through my mind of exactly how to go to the bathroom in this situation. Do I leave them both in the running car (with A/C) while I go into the gas station? Or do I make them get out and stand outside while I do my thing? Should I stop at Taco Bell or the gas station? Mind you, both scenarios have Jordan going into a restroom in a very public place alone.

I seriously wrestled with the decision of what to do for days. I woke up at 4am the day we left having anxiety and almost panic-attacks. You guys, this parenting thing is HARD!

Ice cream + cookie bars can really fix any parenting problem, don’t you think?

(Oh, and we made there and back, stopping both times, and Jordan didn’t get kidnapped. #ThankGoodness)

Last Updated on February 19, 2022

Dorothy Kern

Welcome to Crazy for Crust, where I share recipes that are sometimes crazy, often with a crust, and always served with a slice of life.

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  1. I just finished dinner and was nice and full until I read this and looked at those wonderful pics. Now I’m hungry for dessert already!!! LOL

  2. These look amazing. I recently dealt with a scary situation on a road trip. My husband really had to use the restroom and I was pumping the gas. Then my 6-yr-old daughter decided she had to go too. The baby was asleep in her car seat so I couldn’t leave her alone and of course my husband wasn’t back yet. I was so worried to let her go in alone. It was a gas station in a small town and we didn’t know the area. However, there weren’t many people around who could have taken her. I let her go in and watched through the window. I don’t think I breathed til she came out safely. It turned out fine but I was so worried the whole time.

    1. It’s so scary to let them do things like that!! I hope it gets easier as they get older!

  3. That in between stage sounds like its filled with many decisions! Having a child would send my anxiety out of control! Good thing there are cookie bars 🙂 These look great, pinning them for later!

  4. Oh my goodness, parenting can be so tough. I worry about all those things too and my son is 5 and my daughter is only 2. My husband and I are worrywarts Lol. I know having these bars during those moments would make them so much easier though. They look amazing!

  5. I LOVE that you used peanut butter M&Ms in these! Once the bag is open, those things do not last long in our household (of only two people!!). Evil in the best possible way! Wasn’t sure it was possible to make monster cookies better than they already are! 🙂

  6. I love these bars! Pressing in a pan is so much better than scooping. And your take on parenting gives me some hope for the future. I was my mom’s oldest of 3 girls and I’m pretty sure I was her guinea pig for seeing what worked and what didn’t. She was always pretty laid back and we never got kidnapped 🙂

    1. LOL, that’s how my husband feels except the opposite – he was the baby and by the time they got to him they weren’t as worried!

  7. Oh my gosh do these bars look good. Because monster cookies are the bomb in the first place. But in bar form?! Mmm. I think they’d satisfy even my hyperactive sweet tooth!

  8. The things you worry about…ok my friend, you just need more wine and you won’t worry as much 🙂 I worry and all of parenting feels like blind stabs in the dark some days, but we’re all just doing the best we can do and you’re an amazing mama! With great looking cookie bars that I want!

  9. I totally agree that cookie bars are way easier than parenting, even though I’m not a parent lol. So let’s just stuff our faces with these, right? I love the flavor of these gorgeous bars, Dorothy! Delish!

  10. Parenting has no answers, which means that we spend all our time trying to avoid sending our kids to endless therapy as adults. I have no idea what to do pretty much most of the time, and I also wake up and think about things and can’t sleep. You are not alone!
    And cookie bars? Much easier. And these are heaven. That ice cream on top is such a good idea!!