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Home » Recipes » Bar & Brownie Recipes

Monster Oatmeal Cookie Bars

Published: October 14, 2022 Modified: Dec 4, 2022 by Cambrea Gordon. This post may contain affiliate links.

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monster oatmeal cookie bars on parchment paper.
monster cookie bars on parchment paper.

Monster cookie bars are thick, chewy, and loaded with peanut butter, rolled oats, m&m's, and chocolate chips! They taste like soft oatmeal peanut butter cookies and come together in 30 minutes for an easy dessert that's perfect for any occasion.

monster cookie bars on parchment paper.

I love turning cookie recipes into bar recipes, like cookie dough bars!

These monster cookie bars are basically monster cookies in bar form.

Loaded with peanut butter, rolled oats, and tons of chocolate chips and M&M's, they feature all of your favorites in one pan.

The oats make the bars super chewy, I even took the dough and made iced oatmeal cookies with it!

Warning: they are highly addicting, perfect for sharing (or not sharing), and always a hit!!

For more cookie bar recipes, try Pop Tart Cookie Bars, Nutter Butter Bars, Brown Butter Nutella Bars, and Banana Pudding Brownies.

Jump to:
  • why you'll love this recipe
  • ingredient notes
  • recipe instructions
  • expert baking tips
  • storage & freezing
  • faq's
  • more bar recipes to try
  • Recipe 📖
  • Reviews
three oatmeal cookie bars on their sides to show the inside texture.

why you'll love this recipe

  • Chocolate chip oatmeal bars: This recipe tastes just like a soft and chewy chocolate chip oatmeal cookie but in bar form.
  • Gooey chocolate: These delicious bars are loaded with both semi-sweet chocolate chips and tons of mini M&M's so they have gooey chocolate in every single bite!
  • Easy recipe: If you can make a batch of cookie dough, you can make these cookie monster bars!
  • Basic ingredients: Other than the M&M's, you should have everything you need to make them in your pantry right now.
  • Perfect for any occasion: I love making these cookie monster bars for Halloween and decorating them with candied eyeballs or sharing them as is for any occasion!

ingredient notes

Find the entire ingredient measurements and instructions in the full recipe card below!

ingredients needed to make monster cookie bars.
  • Semisweet chocolate chips: I recommend using semisweet or dark chocolate chips to keep the bars from being too sweet. If you prefer your cookie bars sweeter, you can use white chocolate or milk chocolate chips instead!
  • Old-fashioned or rolled oats: If you don't have any on hand, you can substitute quick-cook oats. It will change the texture of the bars slightly but they work just fine.
  • Peanut butter: These bars are best with creamy peanut butter. I prefer the brands that come already emulsified to ensure there isn't too much oil in the dough.
  • Mini M&Ms: You could also use regular-sized m&m's, whatever you have on hand will work just fine.
a monster cookie bar leaned up against another cookie bar.

recipe instructions

Here's how to make these peanut butter oatmeal cookie bars! You will need a stand mixer or electric hand mixer to make the cookie dough. Before you start, line a square 8x8 baking pan with parchment paper to cover all four sides and set it aside. Then preheat the oven to 350 F/180 C.

STEP ONE: Cream the butter and sugars together. In a large bowl with an electric mixer or in a stand mixing bowl, cream together the peanut butter, room temperature butter, granulated sugar, and dark brown sugar until fluffy.

STEP TWO: Mix in the wet ingredients. Mix in the large egg, egg yolk, and vanilla extract until just combined.

a process collage of the steps for making monster cookie bars.

STEP THREE: Mix in the dry ingredients. Use a rubber spatula to fold in the all-purpose flour, baking soda, salt, mini M&M's, and chocolate chips until just combined.

STEP FOUR: Press the dough into the pan and bake. Transfer the dough to the prepared pan and use an offset spatula to evenly spread it to fill the pan. Sprinkle with more chocolate chips and M&M's on top. You can also decorate them with candied eyeballs for a cute "monster" look! Bake in the preheated oven for 22-23 minutes, or until the edges and top are golden brown and a toothpick inserted into the center comes out just slightly moist.

monster cookie bars on parchment paper.

expert baking tips

  • Use a kitchen scale. Baking with a scale is much more accurate than cup measurements. To convert this recipe, click the "metric" button next to the ingredients title on the recipe card. If you don't own a scale, always spoon-measure your flour. This means fluff the flour with a spoon first, then spoon it into your measuring cup.
  • Additions: Instead of M&M's and chocolate chips you can add heath toffee bar pieces, Reese's pieces, or pretzels.
  • Use different colors for holidays: You can use different colored M&M's for holidays, valentines day, or game day!
  • Baking times may vary: All ovens are different, and your bars may bake quicker or take longer than the indicated baking time. I recommend always checking on them occasionally and testing for doneness!
  • Don't overbake them. If you want nice gooey and chewy bars, bake them just until the top is golden brown and puffy. A toothpick inserted into the center should come out slightly moist but not covered in thick wet dough.
cookie monster bars on parchment paper.

storage & freezing

  • Room temperature: Store leftovers in an airtight container or ziplock bag and keep them on the counter at room temperature. They will stay soft and chewy for 2-3 days. You can also keep them in the baking pan and cover them tightly in plastic wrap.
  • Freezer: Once cut, you can store the oatmeal cookie bars in an airtight container or freezer bag for up to one month.

faq's

Can I make these cookie bars with gluten-free flour?

I have not tested this recipe with gluten-free flour but I would love to hear how they turn out if you try them!

How do I know when they are done baking?

Look for the top of the bars to be golden brown and puffy. After baking it will deflate slightly and leave the edges thicker than the center. This is key for a soft and gooey cookie bar!

Can I make them ahead of time?

Definitely! You can bake these bars the day before eating and freeze them or keep them at room temperature in an airtight container.

a monster cookie bar with a bite taken out of it on parchment paper.

more bar recipes to try

  • Brown Butter Chocolate Chip Blondies
  • Pretzel Brownies with Salted Caramel
  • Blueberry Crumble Blondies
  • Strawberry Lemon Blondies

If you tried this or any other recipe on my website, please let me know how it went in the comments below, I love hearing from you! Also, please leave a star rating while you're there! You can also tag me on Instagram or Facebook so I can check it out!

Recipe 📖

monster cookie bar with a bite taken out of it on parchment paper.
5 from 7 votes
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Monster Oatmeal Cookie Bars

Monster cookie bars are thick, chewy, and loaded with peanut butter, rolled oats, m&m's, and chocolate chips! They taste like one soft oatmeal peanut butter cookie and come together in 30 minutes for an easy dessert that's perfect for any occasion.
Servings 12 bars
Prep 10 minutes mins
Cook 22 minutes mins
Total 32 minutes mins
Course : Dessert
Cuisine : American
Author : Cambrea Gordon
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Equipment

  • square 8x8 baking pan
Need Metric Measurements?Use the button options below to toggle between US cups and Metric grams!

Ingredients 
 

  • 7 tablespoon unsalted butter room temperature
  • ¼ cup creamy peanut butter
  • ¼ cup light brown sugar packed
  • ¼ cup dark brown sugar packed
  • ¼ cup granulated sugar
  • 1 large egg room temperature
  • 1 large egg yolk room temperature
  • 1 tablespoon vanilla extract
  • 1 cup all-purpose flour
  • ¾ cup + â…› cup rolled oats
  • ½ teaspoon baking soda
  • ½ teaspoon salt
  • â…“ cup mini m&ms
  • ½ cup semi-sweet chocolate chips

Instructions

  • Line a square 8x8 baking pan with parchment paper to hang off all four sides. Then preheat the oven to 350 F/180 C.
  • In a mixing bowl, cream the butter, peanut butter, brown sugar, and granulated sugar until light and fluffy.
    7 tablespoon unsalted butter, ¼ cup creamy peanut butter, ¼ cup light brown sugar, ¼ cup dark brown sugar, ¼ cup granulated sugar
  • Mix in the egg, egg yolk, and vanilla.
    1 large egg, 1 large egg yolk, 1 tablespoon vanilla extract
  • Fold in the flour, oats, baking soda, salt, chocolate chips, and mini m&ms
    1 cup all-purpose flour, ¾ cup + ⅛ cup rolled oats, ½ teaspoon baking soda, ½ teaspoon salt, ⅓ cup mini m&ms, ½ cup semi-sweet chocolate chips
  • Spread into the prepared square 8x8 baking pan.
  • Sprinkle more chocolate chips and m&ms over the top if desired.
  • Bake at 350 for 22-23 minutes or until the top is golden brown and a toothpick inserted into the center comes out just barely moist.
  • Let them cool completely on a wire rack before cutting then enjoy!

Video

Notes

Step-by-step process photos are provided above, in the body of this post.
recipe notes
  • Use a kitchen scale. Baking with a scale is much more accurate than cup measurements. To convert this recipe, click the "metric" button next to the ingredients title on the recipe card. If you don't own a scale, always spoon-measure your flour. This means fluff the flour with a spoon first, then spoon it into your measuring cup.
  • Additions: Instead of M&M's and chocolate chips you can add heath toffee bar pieces, Reese's pieces, or pretzels.
  • Use different colors for holidays: You can use different colored M&M's for holidays, valentines day, or game day!
  • Baking times may vary: All ovens are different, and your bars may bake quicker or take longer than the indicated baking time. I recommend always checking on them occasionally and testing for doneness!
  • Don't overbake them. If you want nice gooey and chewy bars, bake them just until the top is golden brown and puffy. A toothpick inserted into the center should come out slightly moist but not covered in thick wet dough.
storage & freezing
  • Room temperature: Store leftovers in an airtight container or ziplock bag and keep them on the counter at room temperature. They will stay soft and chewy for 2-3 days. You can also keep them in the baking pan and cover them tightly in plastic wrap.
  • Freezer: Once cut, you can store the oatmeal cookie bars in an airtight container or freezer bag for up to one month.
Serving: 1serving | Calories: 265kcal | Carbohydrates: 30g | Protein: 4g | Fat: 14g | Saturated Fat: 8g | Polyunsaturated Fat: 1g | Monounsaturated Fat: 4g | Trans Fat: 0.3g | Cholesterol: 49mg | Sodium: 180mg | Potassium: 107mg | Fiber: 1g | Sugar: 20g | Vitamin A: 262IU | Vitamin C: 0.03mg | Calcium: 29mg | Iron: 1mg

The calorie information provided for the recipe is an estimate. The accuracy of the calories listed is not guaranteed.

More Bar & Brownie Recipes

  • Salted Caramel Pecan Bars
  • Cookie Dough Crunch Bars
  • Red Velvet Brownies with Cream Cheese Drizzle
  • Pop Tart Cookie Bars

Reader Interactions

Comments

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    Recipe Rating




  1. Maya says

    December 01, 2022 at 9:15 am

    Hi! I was looking for your recipe for dirt pudding brownies as I was planning on making it but it seems to not be on the blog anymore! Are you reworking it?

    Reply
    • Cambrea Gordon says

      December 01, 2022 at 12:04 pm

      Hi Maya! Unfortunately, that recipe was lost in a few website transitions and it is now lost to the web 😢

      Reply
  2. Frieda Pivon says

    November 01, 2022 at 11:50 pm

    Sorry, I am confused about the metric measurements, 1-2-3 ?? If it’s all for the
    same 8 + 8 size baking pan ? Please help, as I would love to make them
    for my grandkids ?! I need everything in cup measurements. Also, why 2 or 3 eggs ?

    Reply
    • Cambrea Gordon says

      November 02, 2022 at 8:12 am

      The 1-2-3 is strictly for doubling or tripling the recipe. It's default is 1x. If you want everything in cup measurements don't click the metric button. There is only 1 egg in the recipe, not 2-3.

      Reply
  3. Karli says

    October 23, 2022 at 7:07 pm

    5 stars
    So I am NOT a baker but these were soooo easy and SO FREAKING GOOD!!! They were also so cute with the eye ball sprinkles. I'm going to be making this recipe on repeat I already know it.

    Reply
  4. Asma Ahmadi says

    October 21, 2022 at 11:56 am

    5 stars
    These are amazing!!! They turned out perfect and tasted amazing. Thank you for sharing such a great recipe!

    Reply
  5. Lauren says

    October 19, 2022 at 11:01 am

    5 stars
    All of your recipes are amazing but i have to say this one is my new favorite!!! SOOO GOOD 🤤

    Reply
  6. Sam says

    October 19, 2022 at 10:50 am

    5 stars
    Stop what you’re doing and make these immediately!!! Sooooo delicious, chewy, soft, chocolatey, just perfect.

    Reply
  7. Sammie says

    October 14, 2022 at 12:36 pm

    5 stars
    I usually never care for cookie bar recipes because they're either too sweet or not chewy enough. These however were perfect!! I followed the recipe exactly and made sure I read the entire post before baking and they could not have turned out better. So chewy and the middles were actually gooey!

    Reply

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Hi friend, I'm Cambrea!

As a professionally trained pastry chef, I'm sharing bakery-worthy treats both sweet and savory that are unique twists on classic recipes. My reliable recipes are sure to impress any crowd and make all of your dessert dreams come true!

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