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Tuesday made better with Monster Oatmeal Chocolate Chip Cookie Bars for snacking. These one bowl homemade oatmeal cookie bars with chocolate chips and Reese’s Pieces are the perfect way to use up any leftover Halloween candy. They’re super easy, festive for both Halloween and Thanksgiving, and most importantly, everyone LOVES them!

overhead photo Monster Oatmeal Chocolate Chip Cookie Bars with mini pumpkins in photo

It’s been so long since I shared a simple cookie bar. But with Halloween right around the corner, I figured now was the perfect time.

We don’t get trick-or-treaters up here where we are, it’s a little too rural. Asher goes into Frisco where she goes to school and where the businesses on Main Street hand out candy. But she never brings much, if any, home. In general, we really don’t eat candy, and I don’t usually love using candy in my baking recipes. But sometimes, mostly for fun holidays like Halloween and Christmas, I cave in and throw some candy into recipes.

The Halloween candies that we always have a lot of around here…M&M’s and Reese’s Pieces. I tend to buy way more than we’ll actually ever eat. I get so excited when they come out with the fall colors…followed by the holiday colors (I’m such a sucker for any kind of holiday packaging), that I buy one too many bags and never know what to do with them all.

Enter these cookies bars. I mean, it’s Halloween, so I figure, if there’s ever a time to have fun with a candy filled recipe, it’s now. You know?

A simple oatmeal cookie base studded with chocolate chips and your favorite leftover Halloween candy. I used Reese’s Pieces, but M&M’s or your favorite chopped up candy bar would be great too. Use what you, your family, and friends love most.

close up photo of Monster Oatmeal Chocolate Chip Cookie Bars

As you can guess, these are pretty easy to make.

I used my mom’s oatmeal chocolate chip cookie recipe as a base (which is from the HBH cookbook). Then I stirred in some candy pieces (again, use your favorite, chopped Reese’s would be so good too). I also decided to bake the cookies into bars, instead of round cookies. Mom’s recipe is honestly the BEST. Nothing beats it, and the fact that it’s a one bowl and done kind of recipe makes them that much better.

Bonus? I pretty much always have the ingredients on hand. So it’s the perfect recipe to bake up whenever a craving for oatmeal cookies hits. And yes, along with this bar being easy to make, they’re also so delicious. Best oatmeal cookies. Ever.

And I really mean it.

over head photo of Monster Oatmeal Chocolate Chip Cookie Bars with knife and mini pumpkin in photo

I baked these up with my little sister, Asher in mind. She’s been begging me to make cookies. She has a class Halloween party coming up that I promised to bake something for, so we tested these cookie bars out over the weekend. These are full on Asher approved. The thing with kids? They tend to be picky, so I knew I could be getting into trouble with the oatmeal cookie. But I really wanted to bake up something other than just another chocolate chip cookie. Been there done that. I was worried, but when she came down to the studio on Saturday, she ended up loving every bite. She could not get enough.

Granted, she loved the “Halloween” colored candies. But she also said the cookies were delicious. She’s so excited to make them again for her Halloween party.

Side Note: Asher is now ten. When I asked her what she was going to be this year, she said, “you’ll have to wait until Halloween to find out”. And with sass. Ugh. I wish she’d just stop growing up already!

overhead close up photo of Monster Oatmeal Chocolate Chip Cookie Bars

Whenever I make the recipes I grew up baking with my mom, those more classic recipes, I always ask myself, why don’t I bake these more. Obviously it’s because I am constantly testing out new recipes. But it’s a bummer that it’s hard to find time to bake anything that’s “old” and from the archives. I’m glad I decided to dust this recipe off and share it with you guys.

Sometimes I forget that it’s the classic recipes that are really the greatest. Hands down a favorite recipe of the month. And I love that these are fun for both Halloween and Thanksgiving.

overhead photo of Monster Oatmeal Chocolate Chip Cookie Bars with cookies missing from photo

If you make these cookie bars please be sure to leave a comment and/or give this recipe a rating! Above all, I love to hear from you guys and always do my best to respond to each and every comment. And of course, if you do make this recipe, don’t forget to also tag me on Instagram! Looking through the photos of recipes you all have made is my favorite!

Monster Oatmeal Chocolate Chip Cookie Bars

Prep Time 10 minutes
Cook Time 20 minutes
Total Time 30 minutes
Servings: 18 cookie bars
Calories Per Serving: 1732 kcal

Nutritional information is only an estimate. The accuracy of the nutritional information for any recipe on this site is not guaranteed.



  • 1. Preheat the oven to 350 degrees F. Grease a 9x13 inch baking dish with butter or line with parchment paper. 
    2. In a large mixing bowl or the bowl of a stand mixer, mix the oatmeal, flour, brown sugar, granulated sugar, baking soda, salt, canola oil, eggs and vanilla. Beat until the dough is moist and all the ingredients are combined. The dough will be crumbly. Mix in the chocolate chips and 1/4 cup candy pieces.
    3. Press the dough into the prepared baking dish and scatter the remaining 1/4 cup candy over top. Transfer to the oven and bake 18-20 minutes or until the edges are set and the bars are golden. Let cool and then cut into bars. 
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horizontal photo of Monster Oatmeal Chocolate Chip Cookie Bars with mini pumpkins in photo

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    1. Hi Jennifer! Yes, you can use melted butter, but I do prefer to use oil! I hope these turn out amazing for you and please let me know if you have any other questions! xTieghan

  1. 5 stars
    Thanks for the great recipe! I halved it and used 3/4 Cup mini chocolate chips and 1/2 Cup mini m&m’s mixed in, I didn’t need to save any to top it, they showed through just fine. I cooked it in an 8×8 for 25 minutes and it was perfect and delicious!

  2. 5 stars
    These bars are amazing! I didn’t have reeses pieces so I used mini M&M’s and they turned out great! I made them for our family vacation to Hawaii and our kids and kid around us devoured them! My husband loved them too! This is now a bi-weekly staple for lunches at school! Thank you! I probably sent your recipe to 20 people!

    1. I am so glad you loved these! And thank you for passing them along! I hope you had an amazing time in Hawaii! So fun! xTieghan

  3. Question about time in oven. The note for this recipe in your book says to bake the bars for 25-30 minutes, but the online recipe here only says 18-20. Which is correct?

    1. Hi Ryan, this is a different recipe from the one in my cookbook. You should follow these directions for this cookie bar and bake 18-20 minutes. Please let me know if you have any other questions. I hope you love this recipe! Thank you! xTieghan

    1. Hey Jennifer! These bars freeze well once bake, wrapped up tightly for up to 3 months. Please let me know if you have any other questions. I hope you love this recipe! Thank you! xTieghan ??

  4. 4 stars
    These were great and whipped up extremely quickly! Perfect for a treat to have around when a sweet craving hits. I did find the baking time was way off, mine ended up taking about 35 minutes.

  5. These are delicious! I made and took out all the candy (sorry) and added crans and chopped apples and a teaspoon of cinnamon. Nice fall treat!

  6. 5 stars
    These are fantastic! I was a bit skeptical of the oil as I prefer to bake with butter but I am no longer a skeptic. I used peanut butter chips in place of the candies only because I did not have them in my pantry. These were a breeze to make and stored well too.

  7. 5 stars
    Great base recipe – so versatile! Thanks for sharing!
    Would never have thought the oil would churn out such a good bar cookie 🙂
    For the record I used half coconut oil/veggie oil (it’s what I had), and added shredded coconut (didn’t have any m&ms or Reese’s) – absolutely delish! Will make again.
    Bonus? The fastest cookie prep ever.

  8. 5 stars
    These are so good! I wasn’t so sure after mixing them up and they were all oily, just a different look/texture than I’m used too (most cookies use softened butter and so blend differently). I baked them for 5-10 minutes longer than the recipe. My kids and I loved them. I love the chewiness of the oats and the chocolatiness of the chips. Thanks so much!!! P.S. I’ve wanted to try them for months now!

  9. 5 stars
    This is seriously one of the best cookie recipes ever, I put peanut butter m&m’s in with the dark chocolate chips and everyone loved them. Thanks so much for sharing! I am going to attemp to make them into round cookies tonight to make them easier for giving/sharing. I hope I don’t mess them up!

    1. Hey Penny! Any details about how you made this would be helpful. IN general this is a very crumbly cookie bar, so you might not have done anything wrong. Please let me know if you have any other questions. So glad you love this recipe. Thanks so much!! xTieghan ?

    1. Hey Wnedie, If you don’t like canola oil I recommend using melted butter or melted coconut oil. Please let me know if you have any other questions. I hope you love this recipe. Thanks so much! xTieghan