These Monster Cookie Bars are soft, chewy, and so easy to make using just a few simple ingredients! Each bite is filled with oatmeal, peanut butter, chocolate chips and M&M’s. They’re always a favorite and are perfect for parties and potlucks!
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Last summer my sister-in-law served us Monster Cookies in bar form, and I thought it was absolutely genius!
I love cookies, but since they tend to be a bit time-consuming to make, I rarely get them made.
But bar cookies? I can easily do that! No rolling and shaping cookies, no multiple pans needing to be baked. It’s just all very quick and simple!
And to be totally honest, I think these are better as a bar than a cookie too! I make them often and they are always a hit.
What I Love About This Recipe
- Quick and Easy. Not only is the ingredient list simple, but the instructions are too! Even my 11-year-old can make them by herself. The process also goes much faster than traditional cookies.
- One Bowl. Who doesn’t love having fewer dishes to wash?
- Simple Ingredients. Other than the M&M’s, you likely already have all the ingredients in your pantry! But if you don’t have M&M’s, scroll down to the Helpful Tips section below for variations that you can use instead.
- Stores Well. Because these Monster Cookie Bars are so soft and chewy, they don’t dry out quickly at all and will stay fresh for several days. Plus they freeze really well too.
- Great for Large Crowds. These are perfect for potlucks, parties, sports events or family reunions as it makes a large amount. These also freeze well, so they are great for making ahead of time too.
Watch Video: Learn How to Make This Recipe
Monster Bar Ingredients
- Butter. I usually use salted butter, but unsalted will work okay too.
- Sugars. Both brown and white are used.
- Eggs. Helps to bind all of the ingredients together.
- Peanut Butter. This is what makes these bars so nice and moist. I prefer to use creamy in this recipe as crunchy peanut butter tends to make the bars a bit drier.
- Baking Soda.
- Oats. I always use quick oats for these bars, although rolled oats might work too!
- Chocolate Chips. I love to use dark chocolate but obviously, milk or semisweet are delicious as well.
- M&Ms. Classic is my favorite for this recipe, but I don’t know why you couldn’t use other kinds. Although, if you are wanting to avoid gluten, see the note under Helpful Tips below.
How to Make Flourless Monster Cookie Bars
STEP 1: Use an electric mixer to cream the sugars and butter together. Add the eggs and beat until fluffy.
STEP 2: Mix in all the remaining ingredients except for the M&Ms and chocolate chips.
STEP 3: Fold the chocolate chips and candy into the cookie dough.
STEP 4: Spread the mixture onto a greased cookie sheet (see notes below). Bake for 17-20 minutes at 350 degrees. They should be firm when done and looked baked on the top and around the edges. Do not overbake!
STEP 5: Allow the bars to cool in the pan for 1 hour, then slice into squares. If they are not set before slicing, they will tend to fall apart.
Helpful Tips
- Pan Size. For a full recipe of monster bars, use a 13 in. x 18 in. cookie sheet. To make a half batch, use a 9×13 pan and slightly reduce the baking time.
- Natural Peanut Butter. These cookie bars have not been tested using natural peanut butter (the kind made with only peanuts and oil), so I can’t guarantee that they will be delicious if you use that.
- No M&M’s? Simply use more chocolate chips instead! Or try using some peanut butter chips if you prefer.
- Gluten-Free. This recipe is gluten-free as long as the oats you are using do not contain gluten. Crispy M&Ms are not gluten-free because they contain barley malt, but the classic version is.
- Variations. For holidays and special occasions, swap the classic M&Ms for pastel, red and green, or other appropriate colors.
- Make Ahead of Time. Prepare the cookie dough according to the instructions, then refrigerate for up to 2 days. Before baking, allow the dough to come to room temperature on the counter.
- Storing and Freezing. Keep the monster bars in an airtight container for up to 4 days on the counter. To freeze, add the cooled bags to a freezer bag. Separate the layers with parchment paper. Freeze for 2 months. Thaw at room temperature before serving.
More Desserts You’ll Love
- Crazy Chocolate Cake (no eggs, no butter, no milk)
- Blonde Brownies- the best chocolate chip brownie!
- 45 Sheet Pan Desserts that Feed a Crowd
- Healthy Double Chocolate Muffins (with oatmeal and yogurt)
- The Best Oatmeal Chocolate Chip Bars
Monster Cookie Bars Recipe
Ingredients
- 3/4 cups butter, softened
- 3/4 cup white sugar
- 3/4 cup brown sugar
- 4 large eggs
- 2 cups creamy peanut butter
- 2 1/2 tsp. baking soda
- 5 cups quick oats
- 1 1/2 cups chocolate chips (9 oz.)
- 1 cup M&Ms
Instructions
- Cream butter and sugars together. Add eggs and beat until fluffy.
- Add remaining ingredients except for chocolate chips and M&M’s. Mix well.
- Fold in the chocolate chips and M&M’s.
- Firmly spread into a greased cookie sheet, smoothing the top into an even layer. (see Notes below) Bake at 350 for 17 to 20 minutes. Do not overbake! They will not be firm when done but should look baked on the tops and edges.
- Let bars cool in the pan for around an hour, then cut into squares. If you do not let them cool completely, they will not hold together well.
Notes
Crystal Carpenter
These are soo good! Tried them for my daughter’s college grad party a couple weeks ago, and they came out great. Of the 3 cookie bar varieties I made, these monster bars went like hot cakes! I let them sit for several hours in the oven (after oven had cooled off) before I cut them, and they were perfect. Held together but still moist and tasty. Making again this weekend!
Lydia Beiler
Aw, this makes me so happy to hear, Crystal! I’m delighted they were such a hit. And big congratulations to your daughter!
Eileen
I made this and had he same problem that it did not cook in 10 minutes. I tried cooking another 10 minutes and let it sit again. PERFECT. Very tasty.
Lydia Beiler
Thanks so much for taking the time to leave feedback, Eileen! I’m delighted to hear that you enjoyed the bars. And the comment on the baking time made me investigate and I discovered that the 10 minutes was for when I made this recipe in cookie form. When I tweaked it for bar form, I somehow failed to update the time. I’m doing that now! So thank you for commenting about that. Hopefully no one else will need to deal with trying to sort out why their bars seem very undercooked! 🙂
Hailey
Is there suppose to be flour in this that I’m missing? Or maybe not enough oats? Tried this recipe twice and it is way too soft, will not harden. First time I left it for hours second tried cooking longer in case my oven temp was off but still not working out. Not sure what I did wrong but I feel it would work better if there was some flour for how much soft stuff there is (pb and butter)
Lydia Beiler
No, there is not to be any flour. As I mention in the recipe article, these are soft and aren’t meant to get “hard”, just firm enough to hold together. They’re fudgier in texture than crunchy if that makes sense. I’m sorry they aren’t working for you though! Are you using natural peanut butter? I haven’t tested them using that and am not sure if it would affect them badly or not. And are you using quick oats and not rolled oats? I think you could actually use rolled oats but again, I haven’t tested them that way. Other than that, I’m not sure what to tell you as my sister-in-law who I got the recipe from makes them often and hasn’t had problems with the recipe. My recipe photographer made them and loved them…in fact she said it’s replacing the Monster Bar recipe that she previously used. And I make them frequently and have not had any issues either.
Lydia Beiler
Hey Hailey, wanted to update here. After Eileen commented above about the bars taking longer I looked again at my notes and discovered that the 10 minutes was when I was making this recipe in cookie form. When I adjusted it to be bar form, I failed to note the change in time. In fact, my recipe photographer just reminded me that I told her to bake them for 17-20 minutes, which worked perfectly for her.
So my apologies! They definitely shouldn’t take an hour, but they should take longer than 10 minutes!