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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. I made these exactly according to the recipe (I think so, anyway – I’ve read and re-read the quantities several times) and they turned out delicious but nothing like your pictures. The dough wasn’t crumbly at all, and they baked up more like blondies without the visibly oaty texture in your pictures. I did have to bake them a few minutes longer for them to look done, and they’re still perfectly soft and chewy. They are fantastic, I’m just baffled that they don’t look like the pictures! Did you really use a whole cup of oil in the ones in the pictures?

    1. Hi Sarah,
      Thanks for giving the recipe a try, so sorry to hear you had issues. I did use a whole cup of oil. Did you use old fashioned oats or instant? Let me know how I can help! xTieghan

      1. Hi Tieghan – thanks for your reply, and sorry that I didn’t see it until I came back to the recipe to make it again. I still don’t know what the difference was in my batch (I did use old-fashioned oats) but they were a huge hit and my family wants them again, so we’re all good here. : )

    2. I would ditto Sarah’s comments. Mine do not look anything like the pictures. I haven’t had a chance to taste mine yet but I was shocked when I pulled them out. That’s when I saw your comment. I did use old fashioned oats and 1 cup oil. ?

    3. 2 stars
      1 out of 5 in our house liked this recipe. I had some of the same issues as the other reviews. Followed everything exactly and I had to cook it about 40 mins. We thought it had too much oatmeal. Thank you for sharing though.

  2. 5 stars
    Excellent again – I couldn’t find Reece’s piece’s so I used peanut butter M@M’s and I do think Reece’s pieces would have been better but they were still fantastic!

    1. Hey Katherine,
      Happy Sunday! I am thrilled to hear this recipe was enjoyed, thanks so much for making it! xTieghan

  3. Love these bars! Have you ever tired using a Flax Egg to sub for the eggs? I have a vegan friend I’m baking for. Thank you!!

    1. Hi Jaymi,
      Fantastic! I am so glad to hear that this recipe was enjoyed, thanks a lot for giving it a try! Have the best week:) xTieghan

  4. 5 stars
    Made these tonight and they were an absolute hit!! So yummy and love that you can swap out the m&ms for whichever holiday is coming up!

  5. My fitness pal put the calories at 380 per bar. If you cut into 18 pieces. Just thought I’d give a heads up. It’s a lot of calories.

  6. 5 stars
    These were super easy to make and tasted awesome! I took them to a dinner party and they impressed everyone there! I halved the recipe and baked in an 8×8 pan, and it worked well.

  7. 4 stars
    Hi! My husband and I basically only make your recipes! Loved how easy these were. However they didn’t hold together, completely crumbly. I didn’t make any substitution and I cooked a little longer just in case. Not sure what happened!
    Would be delish on ice cream to eat with a spoon!

    1. Hi Kelli! I have not tried these with GF flour, I am sorry about that! If you try, please let me know how it turns out! xTieghan

    1. Hey Katy,
      You will want to use old fashioned oats for this recipe. I hope you love the recipe, please let me know if you have any other questions! xTieghan

  8. 5 stars
    I took your advice and added teaspoons of pb when there was about 5 minutes left to bake. They turned out AMAZING!!!! Thank you so much!!!

    1. Hi Jenn,
      I haven’t tested this with peanut butter, but you could add 1/2 teaspoon dollops at the end. I hope you love the recipe, please let me know if you have any other questions! xTieghan