Satisfy your sweet tooth with this delicious Monster Cookie Bars recipe! Made with Old-Fashioned Oats, Peanut Butter, Chocolate Chips, and colorful M&M Candies, it's the perfect bar cookie recipe for any occasion!
Classic Monster Cookies are one of my favorite treats, as they're colorful and easy to make.
But folks - these chewy Monster Cookie Bars are even EASIER to make, and they fit perfectly into snack boxes!
I'm a massive fan of cookies (obviously), but these Monster Cookies in bar form taste amazing without needing to make cookie dough balls or mind the spacing on the baking sheet.
They're great for snacking, movie nights, or for dessert with a scoop of ice cream!
It's a great alternative to a traditional sheet cake birthday cake, too.
For more yummy dessert bar creations, check out these Hello Dolly Magic Cookie Bars, Buckeye Bars, No Bake Avalanche Bars, and my 4th of July Sugar Cookie Bars!
Try some of my other favorite oatmeal cookies, like Chocolate Chunk Oatmeal Cookies, Mango Oatmeal Cookies, or these Lemon Oatmeal Bars.
Shopping List
Wet Ingredients. Butter, Vanilla Extract, Egg, Peanut Butter
Dry Ingredients. All Purpose Flour, Old Fashioned Oats, Granulated Sugar, Brown Sugar, Baking Soda, Salt
Chocolate. M&M Candies (Mini, Regular, or Both), Semi-Sweet Chocolate Chips, Peanut Butter Chips (Optional)
How to Make Monster Cookie Bars
Preheat the oven to 350 degrees. Spray a 9x13-inch baking dish or baking pan with nonstick cooking spray. You can line the dish with parchment paper instead if you prefer, as this will help with removing the bars.
In a large mixing bowl with a hand mixer, or in the bowl of a stand mixer with the paddle attachment, cream the Butter, Peanut Butter, and White Sugar for 2-3 minutes, allowing the mixture to become light and fluffy.
Add the Egg and Vanilla Extract and continue to cream. Then, mix in the Brown Sugar and cream for 2-3 minutes. Scrape the sides of the bowl as needed to ensure you're using all the ingredients.
Gradually add the Baking Soda, Salt, Flour, and Oats. Mix until combined.
Using a stand mixer on low mix in the Chocolate Chips, Peanut Butter Chips, and M&M candy-coated pieces into the cookie dough.
Hand stir in the chocolate and candy to avoid over-mixing it if you prefer.
Press the monster cookie dough into a prepared pan or baking dish, smoothing the mixture out into an even layer with the back of a spoon or with a rubber spatula.
Bake at 350 degrees for 20-24 minutes, or until the edges are set and lightly golden.
Allow the cookie bar to cool in the pan.
Once completely cooled, slice the bar slab into 24 bars.
FAQs
Yes, you can use quick oats for these monster cookie bars if you need to. That said, I really like the larger old-fashioned oats because they give a better texture to the bars.
Avoid overmixing the monster cookie bar dough, as this will develop the gluten in the flour and can make the bars denser. You can use a mixer in this recipe, but only mix until the ingredients are just combined each time.
Storage & Freezing
Store: Store cooled cookies in an airtight container for up to a week. They are best enjoyed within 2-3 days.
Freeze: Freeze these cookie bars as a slab or in individual bars for up to 3 months. Place parchment paper or plastic wrap between the layers when stacking them to prevent sticking. Freeze in a freezer-safe container or in a freezer bag.
Substitutions & Variations
- Chips. Use any kind of chocolate chips or baking chips for this recipe. My preference is Semi-Sweet or Dark Chocolate Chips, but White Chocolate Chips or Milk Chocolate Chips would work well too, as would Peanut Butter Chips!
- Candy. You can use other types of small candy in these bars, like Reese's Pieces, Red Hots, Whoppers, or another kind of M&M (peanut, peanut butter, or caramel cold brew)!
- Topping. Drizzle some melted chocolate over the top for an extra sweet finish, or frost the cookie bars as I do on my Sugar Cookie Bars with Pink Frosting for a special occasion cookie bar cake!
- Peanut Butter. Use crunchy Peanut Butter to add more texture, or smooth and creamy Peanut Butter for a smoother bar. You can also use Natural Peanut Butter if you have it. Just make sure to stir it up before adding it if the Peanut Butter and Oil have separated.
- Cookie Pie. Use a circular pan to make a Monster Cookie Pie Bar for an alternative birthday or celebration cake like my Festive Cookie Pie Bar.
- Thicker Bars. Using a smaller sheet pan will result in thicker cookies.
Pro Tips
What makes a good cookie? Does it have a soft center and crispy edges, and is it chewy? Each of these makes a great quality cookie. To make perfect cookies every time here are some pro tips.
To find out more, check out my Pro Tips Guide for making the best cookies every time!
Weighing Ingredients.
Baking is a science, and adding too much or too little of any of the ingredients will alter the recipe. Weighing and measuring dry ingredients properly makes a world of difference. Investing in a kitchen scale is ideal. When a kitchen scale is not available, make sure to stir and lift ingredients before scooping them into a measuring cup.
| Volume | Ounces | Grams | |
| All Purpose Flour | 1 Cup | 4½ Ounces | 120 Grams |
| Bread Flour | 1 Cup | 4½ Ounces | 120 Grams |
| Granulated Sugar | 1 Cup | 7 Ounces | 200 Grams |
| Brown Sugar | 1 Cup | 7½ Ounces | 213 Grams |
| Confectionary Sugar | 1 Cup | 4 Ounces | 113 Grams |
Room Temperature Ingredients.
Allow the Butter and Egg to come to room temperature and soften by sitting them on the counter for an hour before you begin baking.
Extra Candy
Always add extra M&M's on top of the cookie slab before baking. This adds extra color to the cookie bars to make an all-round perfect sweet treat!
Cookie Bars.
Over baking bars will make them hard instead of chewy. It's best to pull the bars out of the oven when the edges are only slightly golden.
Cooling Rack.
Allow cookies to cool on the baking sheet for a minute or two before moving them to a cooling rack to cool completely.
- Kitchen Scale. I use this for accuracy in measuring, and it's a lifesaver when it comes to consistent baking.
- Wire Rack for cooling cookies. I like to have at least two cooling racks.
- Mixing Bowls. A Large Mixing Bowl for mixing ingredients and small and medium mixing bowls for other ingredients.
- Cookie Sheet. Most recipes will take two batches to bake. It's great to have multiple baking sheets available.
- Parchment Paper or Silicone Baking Mat. Line the Cookie Sheet with parchment paper for easy cleanup and to prevent sticking.
- Cookie Scoop. A small #60 Cookie Scoop or a Medium Cookie Scoop #50 are great choices for uniform drops of cookie dough.
- Storage Container. An Airtight Container to store cookies or a Ziploc Bag works great too.
- Additional supplies. Measuring Cups and Measuring Spoons along with a silicone spatula, are all helpful.
To find out more, check out my Pro Tips Guide for making the best cookies every time!
Have you tried this Monster Cookie Bar recipe?
Let me know what you think of this cookie bar recipe! Tag @bestcookierecipes on social media so I can see how great your cookies turned out! I would also love to read your comments below. Let me know what you think of these cookies. It really does help!
More Colorful Cookie Recipes
- Lucky Charms Cookies
- Leftover Halloween Candy Bar Cookies
- Circus Animal Cookies
- Spring Flower Cookies
- Pink Velvet Cookies
- Strawberry Magic Bars
- Easy Church Window Cookies
Monster Cookies Bars
Ingredients
- ½ cup Peanut Butter 125g
- ½ cup Butter Softened
- ¼ cup Granulated Sugar 50g
- ¾ cup Brown Sugar 160g
- 1 teaspoon Vanilla
- 1 Large Egg
- ½ teaspoon Salt
- 1 teaspoon Baking Soda
- 1¼ cups All Purpose Flour 150g
- 1 cup Old Fashioned Oats 85g
- ¾ cup Semi-Sweet Chocolate Chips 170g
- ¾ cup M&M's Mini Regular or both
- ½ cup Peanut Butter Chips optional
Instructions
- Preheat the oven to 350 degrees. Spray a 9x13 inch baking dish with nonstick spray and set aside.
- In a large mixing bowl, cream Butter, Peanut Butter, and White Sugar for 2-3 minutes, allowing the mixture to become light and fluffy.
- Add Egg and Vanilla Extract and continue to cream. Then mix in brown sugar and cream for 2-3 minutes. Scrape the sides of the bowl as needed to ensure you're using all the ingredients.
- Gradually add the Baking Soda, Salt, Flour, and Oats. Mix until combined.
- Using a wooden spoon, hand stir the Chocolate Chips, Peanut Butter Chips, and M&M candy-coated pieces into the cookie dough.
- Press the monster cookie dough into a prepared pan or baking dish, smoothing the mixture out into an even layer with the back of a spoon or with a rubber spatula.
- Bake at 350 degrees for 20-24 minutes, or until the edges are set and lightly golden.
- Allow the cookie bar to cool in the pan.
- Once completely cooled, slice the bar slab into 24 bars.
- Store cooled cookies in a sealed container for up to a week. Best if enjoyed within 2-3 days.
Notes
- Store: Store cooled cookies in an airtight container for up to a week. Best if enjoyed within 2-3 days.
- Freeze: Freeze cookies for up to 3 months. Place parchment paper between layers when stacking to prevent sticking.
Nutrition Disclaimer
All nutrition values are approximate and calculated by a plugin and are provided as a courtesy. Adding or subtracting ingredients will change the nutritional value.
Rebecca Johnston
Monster Cookies are always a favorite cookie recipe and making them in bar form is so quick and easy. Loaded with everything sweet and I love the oatmeal texture throughout. Yum!