These soft & chewy monster cookie bars are filled with peanut butter, oats, chocolate chips, and m&m's! Bar cookies are my favorite desserts to make for a crowd because they're quick to make & don't require any scooping!
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Why I Love These Monster Cookie Bars:
- Super chewy! The combination of quick oats & a little bit of corn syrup (or honey!) gives these a super chewy texture.
- Simple ingredients: While you can use rolled oats, I like making monster cookie bars with quick oats since they're less expensive!
- Fan favorite: I based this recipe off my regular monster cookies & chocolate chip cookie bars which are so chewy and perfect for a crowd.
Ingredient Notes & Substitutions
- Quick Oats: These make the bars chewy, and are ultimately what make them hearty monster cookies, so definitely don't omit! Quick oats are affordable & easy to find at the grocery store but you can also use rolled oats (which make them even chewier!).
- Peanut Butter: You want to use regular creamy peanut butter for these rather than all-natural peanut butter (since that's more oily). Furthermore, some brands of creamy peanut butter are more runny than others which can affect how wet the dough is. I've made these with both Kroger off-brand and Skippy and the Skippy results in a stickier dough (which is fine, just a little harder to spread into the pan!).
- All-Purpose Flour: Some recipes use all oats and no flour but I find them to be too crumbly and dry. So I prefer using a mix of flour and quick oats.
- Light Corn Syrup: Adding just a little bit to the dough helps make it chewy and prevents it from being crumbly. You can also swap for a thick honey.
How to Make Monster Cookie Bars
Step 1: Mix Dough
- Preheat oven to 350°F.
- In a large bowl, use an electric mixer to cream unsalted butter (¾ cup, i.e. 1½ sticks), granulated sugar (¾ cup), and light brown sugar (½ cup) for 2 minutes until light in color.
- Add in eggs (2 large), light corn syrup (3 tablespoons), and vanilla extract (2 teaspoons). Mix until combined.
- Add peanut butter (¾ cup) and mix until combined. Stir in baking soda (1 teaspoon) and salt (½ teaspoon).
- Add all-purpose flour (1 ¾ cups) and quick oats (1 ¾ cups) and mix until just combined.
- Mix in chocolate chips (¾ cups) and m&m's (¾ cups). Note that for this step, note that we're only using ¾ cups of chocolate chips & ¾ cups m&m's inside the dough so that we can reserve the other ¼ to sprinkle on top.
Step 2: Press into pan & bake
Drop dough into a greased or parchment-lined metal 9×13" pan and spread until smooth. The dough will be a little sticky, so it's easiest to drop the dough into small pieces instead of adding it in one big blob. Sprinkle the remaining ¼ cup chocolate chips and ¼ cup of m&m's on top and gently press into the dough.
Bake at 350°F for 28-32 minutes until the edges and top are lightly golden brown and the center no longer looks wet. Do not overbake or your bars can get dry and will not be as soft and chewy. You want the cookie bars to be lightly brown on the edges and top. Remove from oven and place entire pan on a cooling rack.
Step 3: Cool & Cut
Allow the cookie bars to cool completely before removing from pan. If you cut the bars when they're still warm, they will be crumbly and fall apart. For the cleanest cuts, they need to be fully cooled and/or slightly chilled before cutting.
Slice into 12-24 squares, then enjoy! To keep fresh, cover pan with saran wrap or place bars in airtight container for up to 3 days (after that they start to dry out).
Tips & Variations
- Add other mix-ins! You can add Reese's pieces, mini peanut butter cups, or any other candy!
- Make them for holidays! I love using the holiday m&m's to make these for Christmas, Valentine's Day, Halloween, or the 4th of July!
- Make a larger batch: You can double the recipe and press into a half-sheet pan to make a large batch!
- Mix into ice cream: There's just something magical about warm cookie bars on top of ice cream. So if you can't wait for them to cool, just dig on in and scoop the warm bars on top!
Frequently Asked Questions:
Yes! I use quick oats since they're cheaper but you can use rolled oats for a chewier texture.
I highly suggest using creamy peanut butter for these rather than all-natural peanut butter (since that's more oily).
I've even found that some brands of regular creamy peanut butter are more runny than others, which can affect how wet the dough is. I've made these with both Kroger off-brand and Skippy and the Skippy results in a stickier dough (which is fine, just a little harder to spread into the pan!).
The corn syrup helps hold everything together and create a chewy & moist texture. Honey is the best substitute, they will just be a little less moist.
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Chewy Monster Cookie Bars
Ingredients
⭐️ Before you begin! If you make this, will you do me a huge favor afterwards and leave a review and rating letting me know how you liked this recipe? This helps my small business thrive so I can continue providing free recipes and high-quality content for you.
Instructions
- Preheat oven to 350°F.
- In a large bowl, use an electric mixer to cream ¾ cup unsalted butter (not margarine), ¾ cup granulated sugar, and ½ cup light brown sugar for 2 minutes until light in color.
- Add in 2 eggs, 3 tablespoons light corn syrup, and 2 teaspoons vanilla extract. Mix until combined.
- Add ¾ cup creamy peanut butter and mix until combined. Stir in 1 teaspoon baking soda and ½ teaspoon salt.
- Add 1 ¾ cups all-purpose flour and 1 ¾ cups quick oats and mix until just combined.
- Mix in 0.75 cup semi-sweet chocolate chips and 0.75 cup m&m's. Note: For this step, note that we're only using ¾ cups of chocolate chips & ¾ cups m&m's inside the dough so that we can reserve the other ¼ to sprinkle on top.
- Drop dough into a greased or parchment-lined metal 9x13" pan and spread until smooth. The dough will be a little sticky, so it's easiest to drop the dough into small pieces instead of adding it in one big blob. Sprinkle the remaining 0.25 cup semi-sweet chocolate chips and 0.25 cup m&m's on top and gently press into the dough.
- Bake at 350°F for 28-32 minutes until edges and top are lightly golden brown and the center no longer looks wet. Do not overbake or your bars can get dry and will not be as soft and chewy. You want the cookie bars to be lightly brown on the edges and top. Remove from oven and place entire pan on a cooling rack.
- Allow the cookie bars to cool completely before removing from pan. If you cut the bars when they're still warm, they will be crumbly and fall apart. For the cleanest cuts, they need to be fully cooled and/or slightly chilled before cutting.
- Slice into 12-24 squares, then enjoy! To keep fresh, cover pan with saran wrap or place bars in airtight container for up to 3 days (after that they start to dry out). See notes below for freezing tips.
Notes from Melissa
- Chocolate chips: While I use semi-sweet chocolate chips, you can also use milk, dark, or white chocolate!
- To freeze: To freeze, cool the bars completely before placing them into an airtight container or freezer bag for storage. These will keep in freezer for 1-2 months.
good.
Thank you so much for leaving a review, Elizabeth!
Fun recipe!!! I used the honey substitution and the batter was very thick so I was worried it wouldn't turn out right, but they are very good!!!!! They are much better fully cooled down rather than slightly warm, the oats add great texture and structure. Could use more vanilla for sure, if I remake these I will probably use 1-2 tablespoons and hope that the oats can soak up the extra liquid.
Thank you so much for taking the time to leave a review, Nadia! So glad to hear you enjoyed the recipe!
Very good bar! I substituted gluten free flour ( King Arthur cup for cup) and turned out yummy! Spread dough in 12x17 parchment lined cookie sheet- baked for 20 minutes- perfect! Also- love the recipe directions including amounts!!
Thank you so much for leaving a review, Terri!
Turned out great ! Love love the recipe write out , it’s the easiest one I’ve followed .
Thank you so much for leaving a review, Holly! I really appreciate it!
Going to make this today and hope using almond butter instead of peanut doesn’t affect the outcome too much! My daughter cannot eat peanuts so let hope lol. Thanks for the recipe!
I made these as Peanut Butter Monster Bars with Reese's pieces, mini Reese's PB cups, peanut butter chips, abs chocolate chunks! Anazing!!!
Yumm, that sounds like some great substitutions! Thank you so much for leaving a review, Tracie!
Amazing! I made with the rolled coats and mini M&Ms and chocolate chips.
Thank you so much for leaving a review, Madison!
These were DELICIOUS! 😍 I made them for the July baking challenge for my sisters baby shower, and only 2 were left out of 30! I added Reese’s cups to the top of the cookies before cooking. Any candy will be wonderful on these!
Yay, so glad you loved the recipe, Kirsten! Thank you so much for participating in the July baking challenge and for taking the time to leave a review! :)
The grandkids loved these and so much easier than cookies.
So glad everyone loved this recipe! Thank you so much for leaving a review, Lisa!
Love these bars! We made them for the July Baking Challenge and customized them with 4th of July themed candies. The oats give them a nutty flavor and they are the perfect amount of chewiness. So easy and delicious!
Yay, so glad you loved this recipe, Adrienne! Thank you so much for taking the time to leave a review, I really appreciate it!
Made for baking challenge and they were a hit at my family reunion!
Great to hear everyone loved this recipe, Alison! Thank you so much for leaving a review and for participating in the July baking challenge! :)
These cookie bars are so scrumptious! I made them without the oats as part of this month’s baking challenge, and they were still so delicious. They tasted like a perfect chocolate chip cookie with nutty undertones, love them!!
So glad you enjoyed the recipe and they turned out without the oats! Thank you so much for leaving a review and for participating in this month's baking challenge, Claudia! :)
I made these bars for the July Baking Challenge. This recipe is easy and does not disappoint! My favorite feature is the ability to customize for any holiday!
So glad you loved the recipe, Tomma! Thank you as always for taking the time to try out my recipes and leave a review! :) And thank you for participating in the July Baking Challenge!
Lovely recipe I especially like the peanut butter and oatmeal in it!
So glad you enjoyed the recipe, Mark! Thank you so much for leaving a review!
Did these as part of the July challenge! These were perfect for our Fourth of July party! So moist and perfectly balanced peanut butter and chocolate
So glad you loved the recipe, Shannon! And thank you for leaving a review and for participating in this month's baking challenge! :)