You'll love these quick and easy monster cookie bars! They are soft, chewy and full of peanut butter, oats and chocolate. The best part is they mix up in one bowl by hand!
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Who loves cookies, but needs something quick and easy to bake? I know you are busy bakers too and this monster cookie bars recipe makes the BEST thick, soft and chewy bars!
My recipe doesn't skimp on the peanut butter either. With peanut butter in the dough and then a layer of peanut butter baked between the layers and m&m's and chocolate chips; they are truly a monster cookie dream!
For other stuffed bar cookies try my sugar cookie sandwiches or carrot cake sandwich cookies.
why you will love these easy bar cookies
- Thick and chewy ~ full of oats, peanut butter and chocolate chips. They also have a layer of extra peanut butter in the middle, which makes them gooey and addictive!
- Easy dessert bars ~ everything mixes up in a bowl with a spoon and bakes in one pan.
- One bowl recipe ~ I'm always trying to find ways to use less dishes!
what are monster cookies made of?
Monster cookie bars are a combination of peanut butter, oats, m&m's and chocolate chips {or other mix-ins}. They are soft, thick and chewy and very delicious!
If you need a gluten free {or nut free} version of monster cookies, try my flourless monster cookies.
🥜ingredients and substitutions
Please scroll to the printable recipe card at the end of this post for the full list of ingredients and baking directions.
- Peanut butter ~ Creamy, no-stir peanut butter is best for this recipe. I recommend using a commercial brand like Jif or Skippy. It's used in the monster cookie bars dough and frozen into a layer that gets stuffed between the dough for a gooey middle.
- Melted butter ~ unsalted is my choice, but if you only have salted just leave out the kosher salt.
- Sugar ~ both granulated and brown sugars are used.
- Egg ~ one large egg is needed. I prefer it room temperature, but it isn't going to make or break the recipe if it's cold from the fridge.
- Vanilla ~ pure vanilla extract adds a nice layer of flavor to these bar cookies.
- Kosher salt ~ helps to balance the flavors. Use half the amount if you have table salt.
- Ground cinnamon ~ adds another flavor layer.
- Baking soda ~ just a little to give the chewy bars a little lift.
- Oats ~ old-fashioned oats are what tends to be traditional in monster cookie bars. They add so much chewy texture! I tested this recipe with all old-fashioned oats and with a combination of quick oats and old-fashioned oats. My testers preferred the combination.
- All-purpose flour ~ use your favorite brand and be sure to measure correctly. If you need gluten free bar cookies a 1 to 1 gluten free flour blend will also work.
- Chocolate chips and m&m's ~ my family likes semi-sweet chocolate chips, white chocolate chips and mini m&m's. Peanut butter chips, Reeces Pieces and toffee bits are all excellent choices for mix-ins too.
prep the gooey peanut butter layer
Prepare an 8x8 baking pan with parchment paper {or aluminum foil}, drop the peanut butter into the prepared baking pan and smooth into an even layer. Pull the peanut butter out of the pan and place on a small cutting board to flat surface and place in the freezer for a minimum of 1 hour and up to 2 days.
👩🏼🍳how to make these easy thick and chewy bars
Once the peanut butter layer has frozen, preheat the oven and prepare an 8x8 baking pan with parchment paper.
In a medium to large bowl, mix together the melted butter and peanut butter until well combined.
Now add the brown sugar and granulated sugar and stir until combined.
Then add the egg and vanilla. Scrape up and down the bowl if needed and mix until combined.
Now add the cinnamon, baking soda and kosher salt and mix until well combined.
Next add the oats and all-purpose flour and mix until some large flour streaks remain. Then add your mix-ins and gently fold to combine.
Drop half of the cookie dough into the prepared baking pan and smooth to an even layer.
Then remove the peanut butter layer from the freezer and gently peel it off the parchment paper and lay it over the top of the dough. I found the peanut butter can stick in a few places, but should mostly pull off. In my testing it sticks to aluminum foil more than parchment paper. Gently spread the remaining dough over the top of the peanut butter layer. Add a few extra mix-ins pressed on top, if desired.
Bake for 20 - 25 minutes or until the edges have lightly browned and a tester in the center comes out with just a few moist crumbs. Allow to cool in the pan on a wire cooling rack.
Remember to pin this recipe to Pinterest! Use the button on the recipe card or the share buttons on the side or bottom of this page.
tips for the best monster bar cookies
Remember that your oven is different than mine and baking times may vary slightly.
Measure your oats and flour correctly. A kitchen scale is best, but if you don't have one use the spoon and level method. Spoon the flour or oats into the measuring cup and use the back of a knife to level it off.
Don't over bake! For the best soft and chewy with a gooey peanut butter middle, don't over bake these bar cookies.
The frozen peanut butter layer should peel off the parchment paper in mostly one piece. If it breaks, it's okay, just do your best to lay it into an even layer over the cookie dough.
For a bakery style looking cookie bar save aside a tablespoon of the mix-ins and press them into the top of the cookie dough prior to baking.
variation ideas for this one bowl recipe
- Halloween ~ use Reeces Pieces and eye ball candies.
- Triple peanut butter ~ use peanut butter chips and Reeces Pieces for mix-ins.
- Use colored m&m's to match your favorite sports team or holiday.
- Chop up leftover Halloween candy into small pieces for your mix-ins.
- To make them extra chewy, add some coconut.
frequently asked questions
are monster cookie bars gluten free?
This recipe, as written, is not gluten free. But you can replace the flour with a 1 to 1 gluten free flour replacement {I like King Arthur or Bob's Red Mill} and make sure your oats are certified gluten free for a gluten free version.
what kind of peanut butter do I need?
Creamy, no-stir peanut butter is best for this recipe. I like Skippy or Jif.
Can I use quick oats?
I tested this recipe with 100% old-fashioned rolled oats. I also tested this recipe with 50% quick oats and 50% old-fashioned oats; my taste testers preferred the combination of old-fashioned and quick oats.
can I bake in a different size pan?
Yes, you can use a 9x9 baking pan. Just know the bars will be a little thinner and will need a little less time to bake.
You can also double the recipe and bake them in a 9x13 pan.
how to store
Monster cookie bars will stay fresh in an airtight container at room temperature for 2-3 days or can be stored in an airtight container in the refrigerator for up to 5 days. We like them best at room temperature.
They also freeze well for up to three months; allow to defrost before serving.
Remember to snap a picture and tag me @twosugarbugs on Instagram if you make these Monster Cookie Bars. It warms my heart to see you bring these recipes to life! Thank you for being here and happy baking!
more peanut butter recipes
- Peanut Butter Muffins
- Butterfinger Pie
- No Bake Peanut Butter Espresso Cheesecake
- Buckeye Bars
- Peanut Butter Thumbprint Cookies
If you make this recipe {or any recipe!} from two sugar bugs please come back and leave a review and a ⭐️⭐️⭐️⭐️⭐️ star rating. I read every comment, and I LOVE hearing from you!
Monster Cookie Bars
recipe created and tested by:
I highly recommend using weight (metric) measurements when available for more accuracy and the best results.
Please note
When using 2x or 3x ingredients, the grams DO NOT adjust, you will have to manually do that.
Ingredients
- ½ cup peanut butter 120g
- ¼ cup unsalted butter melted 57g
- ½ cup peanut butter 120g
- ½ cup packed brown sugar 100g
- ¼ cup granulated sugar 50g
- 1 large egg
- 2 teaspoons pure vanilla extract
- 1 teaspoon ground cinnamon
- ½ teaspoon baking soda
- ½ teaspoon kosher salt
- 1 ¼ oats* 100g
- 1 cup all-purpose flour 125g
- 1 cup mix-ins I used semi-sweet chocolate chips, white chocolate chips and mini m&m's
Instructions
for the peanut butter filling
- Prepare an 8x8 baking pan with parchment paper (or aluminum foil), drop the peanut butter (½ cup/120g) into the prepared baking pan and smooth into an even layer. Then use an off set spatula or knife to push the edges in slightly. Pull the peanut butter out of the pan and place on a small cutting board to flat surface and place in the freezer for a minimum of 1 hour and up to 2 days. (If placing in the freezer longer than 1 hour, cover the peanut butter layer).
- Preheat oven to 350°F and line a 8x8 baking pan with parchment paper.
for the cookie bars
- In a medium to large bowl, mix together the melted butter (¼ cup/57g) and peanut butter (½ cup/120g) until well combined.
- Now add the brown sugar (½ cup/100g) and granulated sugar (¼ cup/50g) and stir until combined.
- Then add the egg (1 large) and vanilla (2 teaspoons). Scrape up and down the bowl if needed and mix until combined. Now add the cinnamon (1 teaspoon), baking soda (½ teaspoon) and kosher salt (½ teaspoon) and mix until well combined.
- Next add the oats* (1 ¼ cups/100g) and all-purpose flour (1 cup/125g) and mix until some large flour streaks remain. Then add your mix-ins** (1 cup total) and gently fold to combine.
- Drop half of the cookie dough into the prepared baking pan and smooth to an even layer. Then remove the peanut butter layer from the freezer and gently peel it off the parchment paper and lay it over the top of the dough. I found the peanut butter can stick in a few places, but should mostly pull off. In my testing it sticks to the aluminum foil more than parchment paper. Gently spread the remaining dough over the top of the peanut butter layer. Add a few extra mix-ins pressed on top, if desired.
- Bake for 20 - 25 minutes or until the edges have lightly browned and a tester in the center comes out with just a few moist crumbs. Allow to cool in the pan on a wire cooling rack.
- Then use the parchment to pull the bars out of the pan and cut into desired sizes.
Notes
Nutrition
The nutrition information is based on third-party calculations, is an estimate only and may not be entirely accurate. Actual nutritional values will vary based on brands used and portion sizes.
Jennie says
I'm confused. In the list of ingredients you listed 1/4 cup of butter melted but in the directions you stated a1/2 cup.
Tasia says
Hi Jennie, thank you for catching that. It is a 1/4 cup butter and I have corrected the directions.
Linda says
Made these cookie bars today and they are to die for. Thank you for a new favorite!
Tasia says
Hi Linda, thank you for making my recipe and coming back to leave a comment. I am so happy you loved them!
Ben | Havocinthekitchen says
These cookie bars may be called monster but they are not monstrous at all but stunning and appealing. Gosh - never had so many delicious flavours and textures in one cookie/bar. Wonderful texture, too!
Tasia says
Aww, thank you for the lovely review Ben!
Ashleigh F says
These were so, soo good! They were quick to come together and baked up beautifully. 10/10! I’ll definitely be making these again soon!
Tasia says
Hi Ashleigh, thank you for coming back to leave a review. I am so happy you loved these cookie bars!
TJ says
Perfect Saturday night movie snack! They were soft and chewy and yummy.
Jody says
in the ingredients list it mentions 1/2 cup peanut butter twice.
Tasia says
Hi Jody, the first half cup of peanut butter is frozen to form the middle peanut butter layer. The second listing of peanut butter is used in the cookie dough, so you need them both to execute the recipe.