Monster cookie bars are chewy ooey gooey thick bars! They’re loaded with peanut butter, m&m’s, rolled oats, and chocolate chips! It’s the kind of recipe you make when you don’t feel like rolling out cookies but still want a soft oatmeal peanut butter cookie!
These monster cookie bars are basically like monster cookies but in bar form! They come together in 30 minutes to satisfy your cravings nearly immediately! If you don’t have a cookie tray or don’t feel like rolling out cookies, this is the perfect recipe to make.
These bars are full of rolled oats, creamy peanut butter, m&m’s, and chocolate chips! It’s made in one bowl, and no electric mixer is needed! Of course if you’d like to use one it does speed up the process.
Why this recipe works
Easy to make: No mixer needed and it comes together in one bowl.
Oatmeal bars: This recipe tastes just like a soft and chewy oatmeal cookie but in bar form.
Chocolate goodness: These bars are loaded with chocolate chips and mini m&m’s! The best combo.
Perfect for any occasion: This recipe is super flexible for any occasion. The little monster eyes placed on top are the cutest for halloween, but you can leave them out or change it to any holiday sprinkles!
Kids friendly dessert: A fun halloween recipe to make with young kids that isn’t too scary but rather ‘cute’!
Scroll to view a few ingredients notes. Full recipe and measurements can be found in the recipe card below.
Butter – Unsalted butter works best. This will be softened to room temperature. Remove two hours before baking
Chocolate chips – I used semi-sweet, but mini or dark works too. Don’t use milk or it’ll be too sweet.
Dark brown sugar – This type of brown sugar carries more molasses than lighter brown sugars, which helps create chewy cookie bars.
Eggs – Must be room temperature. The egg yolk helps add extra softness and moisture. Remove from refrigerator two hours prior to baking.
Mini M&M’s – I bought mini M&M’s at my local grocery store. Sometimes they are tricky to find, so you may use regular sized too.
Peanut butter – Must be creamy peanut butter. Natural is too runny. Crunchy works as well!
Step by Step Instructions
Here is how to make and bake these monster cookie bars. They come together in one bowl with a whisk or an electric mixer. An electric mixer will speed up the process and save you elbow grease.
Step 1: Mix the butter and sugars: In a large mixing bowl, cream butter, peanut butter, and both brown sugars until light and fluffy.
Step 2: Add in egg and vanilla. Whisk in the egg yolk, egg, and vanilla until smooth.
Step 3: Add in dry ingredients. Fold in flour, rolled oats, baking powder, and salt. The dough will be very soft.
Step 4: Toss in add-ins. Add in the mini M&Ms and chocolate chips.
Step 5: Press the dough into the pan and bake. Transfer the dough to the prepared pan and use a spatula to evenly spread it in the pan. Bake in the preheated oven for 20-21 minutes, or until the edges are a light golden brown.
Step 6: Decorate and slice. Once baked, add extra add-ins if desired. You can also decorate them for halloween using candy eyeballs for a cute monster look! Slice and enjoy!
Expert baking tips
Here are a few baking tips from my kitchen to yours
- Properly measure the flour by spooning the flour into the measuring cup. If you stick the measuring cup directly into the bag of flour, it will compact it and you will have more than you need. A digital scale will give you the most accurate results.
- Substitute the add-ins! You can use any kind of chocolate chips, toffee pieces, regular-sized M&M’s, peanut butter filled M&M’s, etc!
- Add the halloween decor eyes on after they’ve been baked and sliced.
- Soften the butter quickly by placing it in the microwave at 15 second intervals or into the oven at 170°F for 2 minutes.
- It’s better to underbake than overbake. The bars will continue to bake as they cool.
Can I use regular sized M&M’s?
Can I double this recipe?
Yes! Use a 9×13 pan when doubling.
Can I use quick oats?
Yes! But keep in mind the texture will change.
Can I use one type of brown sugar?
Yes. If you only want to use one type, make sure to use 1/2 cup. (Rather than 1/4 cup light and 1/4 cup dark).
How do I know they’re done?
The bars will be a light golden brown on the edges. The middle will look soft. If you remove them from the oven immediately they will slightly deflate.
How do I store these monster cookie bars?
Keep on the counter for 3 days or refrigerated in an airtight container for up to 5 days.
Check out these recipes
- Single Serve Triple Chocolate Cookie
- Double Chocolate Condensed Milk Cookies
- White Chocolate Reese’s Pieces Peanut Butter Cookies
- White Chocolate Toffee Cookies
Monster Cookie Bars
- 1/2 cup butter softened
- 1/3 cup peanut butter creamy
- 1/4 cup dark brown sugar
- 1/4 cup golden brown sugar
- 1 egg room temperature
- 1 egg yolk room temperature
- 1 1/2 tbsp vanilla
- 1 cup all-purpose flour
- 1 cup rolled oats
- 1/2 tsp baking powder
- 1/4 tsp salt
- 1/2 cup mini m&ms
- 1/2 cup semi-sweet chocolate chips
- halloween decor eyes optional
- Preheat the oven to 350°F/180°C. Line a square 8×8 baking pan with parchment paper and set aside.
- In a large mixing bowl, cream butter, peanut butter, and both brown sugars until light and fluffy.1/2 cup butter, 1/3 cup peanut butter, 1/4 cup dark brown sugar, 1/4 cup golden brown sugar
- Add in the egg, egg yolk, and vanilla and continue whisking.1 egg, 1 egg yolk, 1 1/2 tbsp vanilla
- Add in the flour, baking powder, rolled oats, and salt. Fold until a soft dough forms. Do not overmix!1 cup all-purpose flour, 1 cup rolled oats, 1/2 tsp baking powder, 1/4 tsp salt
- Toss in the chocolate chips and mini M&M's and mix until just combined.1/2 cup mini m&ms, 1/2 cup semi-sweet chocolate chips
- Transfer into the prepared baking pan and press down firmly and evenly.
- Bake for 20-21 minutes or until the edges are a light golden brown. The middle will look soft, but will continue to bake as it cools
- Add more chocolate chips, M&M's, and some halloween decor if desired. Slice and enjoy!halloween decor eyes