Monster Cookie Bars
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Monster Cookie Bars are filled with old-fashioned oatmeal, peanut butter, chocolate chips, and mini M&M’s – and make the best treats. These easy bars are quick to make and require no chill time!
Making bars is definitely no fuss. For other cookie bar recipes, be sure to try our Chocolate Chip Peanut Butter Blondies, the best Frosted Sugar Cookie Bars, and some fun S’mores Cookie Bars!
M&M Cookie Bars
My mom made the best M&M monster cookies and loved making them extra large. They were impressive for sure, and I’ve given the recipe to numerous people over the years, even before I started the blog. So this recipe is just a version of those but in bar form. Here’s what I did.
- Bought a new 9×13 USA pan (linked below) and made it fit.
- Adjusted the monster cookie recipe because that’s a big one and I wanted them to bake well. (Not too thick and not too thin.)
- Used mini M&Ms and mini chocolate chips instead of regular-sized for these chewy bars.
Why We Love These Bars:
- SIMPLE TO MAKE. These require no chill time before baking, and you’ll need just one pan. No baking multiple batches of cookies!
- DELICIOUS. Just like the classic monster cookies, these bars are tender, chewy, and full of chocolate and peanut butter. So much to love and a real crowd pleaser!
- FREEZE WELL. You can make this perfect treat ahead of time, stick them in an airtight container, and freeze for a couple of months. Be sure to use some parchment paper in between layers of bars.
NO FLOUR! These delicious monster cookie bars do not include flour. If you want gluten-free bars, be sure to use gluten-free oats.
Ingredients Used:
You’ll need classic pantry ingredients for this monster cookie bars recipe. You can also use substitutions, like using crunchy peanut butter instead of creamy, quick oats instead of old fashioned, and regular-sized chocolate chips and M&Ms instead of mini versions.
- Butter – I always use unsalted butter, but you could use salted butter if you’d like.
- Sugars – A combo of brown sugar and granulated sugar is a perfect balance.
- Eggs – Two large eggs are required.
- Peanut Butter – I normally use creamy peanut butter, but crunchy would also be excellent here.
- Vanilla – I keep Watkin’s Pure Vanilla extract at the ready at all times.
- Baking Soda – Used to leaven the bars.
- Oatmeal – Plenty of old-fashioned oatmeal gives these bars a chewy texture.
- Kosher Salt – Just a pinch.
- Chocolate Chips – Mini chocolate chips.
- M&Ms – Mini M&Ms. Don’t forget to add a few extra to the top of the bars!
How to make Chewy Monster Cookie Bars:
I recommend using a kitchen scale to weigh the ingredients instead of using a measuring cup, for best results. Always use room temperature ingredients.
Step 1
Prep. Preheat your oven to 350 degrees. Prep a 9×13 pan with parchment paper, if desired. You can also just spray the pan with baking spray.
Step 2
Mix. In the bowl of a stand mixer, cream the butter and sugars together. Add the eggs, peanut butter, and vanilla, and mix again. Then add the dry ingredients – the baking soda, salt, and rolled oats – and mix again. Finally, fold in the chocolate chips and M&M’s by hand.
Step 3
Assemble. Spread the cookie mixture evenly into all sides of the pan. Press down gently to get a uniform layer.
Step 4
Bake. Bake for 25 minutes or until slightly golden brown on top. If you want them to be more gooey, bake for less time. Let them cool for about 10 minutes if using parchment paper (and if you want to lift them out of the pan).
Step 5
Serve. Serve bars with a scoop of ice cream or with a tall glass of milk!
Storing and Freezing Monster Cookie Bars:
- Storing – Place bars in an airtight container and store on the counter for three to four days.
- Freezing – You can freeze these for up to two months. But I suggest either eating them or sharing them with neighbors and friends instead! I actually love sending goodies to Mike’s work and they get devoured quickly.
- Freezing dough – You can freeze the monster cookie dough and make it fresh for any occasion.
Recipe Variations:
- Instead of M&Ms, try using Reese’s Pieces, dark chocolate chips, peanut butter chips, or butterscotch chips.
- You could also try adding chopped-up peanut butter cups, leftover Halloween candy, or any candy bars.
Other Oatmeal Cookies:
While we love a regular chocolate chip cookie, oatmeal cookies have a special place in our hearts (or bellies!). Here are some of our favorites.
Monster Bars Recipe Tips:
- Be sure to use full-fat regular peanut butter. Using natural peanut butter will not produce the same consistency in these and you’ll be left with a dry bar.
- Feel free to play around with other mix-ins. You could try different flavored chips, toffee bits, any kind of nuts, or candies.
- You can also use quick oats if preferred. It’s basically the same oatmeal but in smaller crumbs instead of whole oats.
- If you like a gooey cookie, you can decrease the cooking time. I like these browner on top but feel free to make them the way YOU like.
Kitchen Tools Used: (affiliate links)
xoxo ~Sue
Monster Cookie Bars
Ingredients
- 6 Tablespoons unsalted butter – softened
- 1 ¼ cup brown sugar (275 grams)
- 1/2 cup granulated sugar (100 grams)
- 2 large eggs
- 1 cup peanut butter (270 grams)
- 1 teaspoon vanilla extract
- 1 ½ teaspoons baking soda
- 3 cups old fashioned oatmeal (240 grams)
- 1/2 teaspoon kosher salt
- ¾ cup mini chocolate chips
- ¾ cup mini M&Ms
Instructions
- Prep. Preheat your oven to 350 degrees. Prep a 9×13 pan with parchment paper, if desired. You can also just spray the pan with baking spray.
- Mix. In a large standing mixer, cream the butter and sugars together. Add the eggs, peanut butter, and vanilla, and mix again. Then add the dry ingredients – the baking soda, kosher salt, and oatmeal – and mix again. Finally, fold in the chocolate chips and M&M's. I normally do this by hand.
- Spread the cookie mixture evenly into all sides of the pan. Press down gently to get a uniform layer.
- Bake for 25 minutes or to your liking. If you want them more gooey, bake for less time. Let them cool for about 10 minutes if using parchment paper (and if you want to lift them out of the pan).
- Serve bars with a scoop of ice cream or with a tall glass of milk!
Notes
- Storing – Place bars in an airtight container and store on the counter for three to four days.
- Freezing – You can freeze these for up to two months. But I suggest either eating them or sharing them with neighbors and friends instead! I actually love sending goodies to Mike’s work and they get devoured quickly.
Such a delicious and easy to make recipe. They almost seem healthy and making as bars they can be ready in no time. Will make again soon.
Thank you Shari!
Each bite is delicious! Love these!
Thanks Holly! 🙂
I am a system expert on monster cookies and these are the best ever. Pro tip is to always start with eating the cookie in the middle.
Haha, you’re funny!