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 soft oatmeal peanut butter cookies and come together in 30 minutes for an easy dessert that's perfect for any occasion.

These are the best monster cookie bars ever!!

If you love monster cookies, you'll love this dessert. They're 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.

I love this cookie bar recipe when I'm feeling super lazy and not wanting to scoop or chill dough. They are easily made in one bowl and are out of the oven in 30 minutes! They have the best chewy and gooey texture and aren't overly sweet like most cookie bars so I know you are going to love them!

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

For more cookie bar recipes, try 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

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!

• 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.

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.

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.

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.

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

more bar recipes to try

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 📖

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