These soft, chewy Monster Cookie Bars are packed with peanut butter, oats, chocolate chips, and colorful M&Ms. This easy recipe feeds a crowd and bakes in under 30 minutes—no scooping required!
A Monster of a Cookie Bar!
This one's sure to please! Today I’m sharing something extra fun — Monster Cookie Bars, loaded with hearty, sweet flavors. These bars are perfect for bake sales, potlucks, school parties, or anytime you need a dessert that delivers rich, nostalgic flavor and big, bold color.
Whether you’re baking for a crowd, avoiding allergens, or just want options, you’re going to love both of these easy cookie bar recipes.
What Are Monster Cookie Bars?
Monster Cookies traditionally combine:
- creamy peanut butter
- oats
- chocolate chips
- colorful M&Ms
They’re hearty, chewy, and packed with flavor. These cookie bars take everything you love about Monster Cookies and bake them in a single pan — no scooping required.
At a Glance
Skill Level: Easy
Main Flavors: Oats, chocolate, M&Ms, optional peanut butter
Includes: Classic PB version + Peanut-free version
Best For: Parties, school events, church gatherings, holidays, bake sales
Master Cookie Bar Ingredients
You'll find a full printable recipe card at the bottom of this post but here's a glance at what you'll need. These are simple ingredients you might already have in your kitchen.
Wet Ingredients
- 1 cup butter, softened (salted or unsalted, your choice)
- 1 cup brown sugar, packed
- 1 cup granulated sugar
- 1 ½ cups creamy peanut butter
- 3 large eggs
- 1 tablespoon vanilla extract
Dry Ingredients
- 2 cups quick oats
- 1 ½ cups all-purpose flour
- 1 teaspoon baking soda
- ½ teaspoon salt
Mix-Ins
- 1 cup chocolate chips
- 1–1½ cups M&Ms (plus more for topping)
How to Make Monster Cookie Bars
These come together so easily! You're going to love making them, I promise. (It brings out the child in you, for sure!)
Preheat and Prepare Pan
Preheat oven to 350°F.
Line a 9×13 baking dish with parchment or spray lightly with baking spray.
Cream the Butter, Sugars & Peanut Butter
Beat together butter, brown sugar, white sugar, and peanut butter until smooth and fluffy.
Add Eggs and Vanilla
Mix in eggs one at a time.
Stir in vanilla extract.
Combine Dry Ingredients
Whisk oats, flour, baking soda, and salt.
Mix Wet + Dry
Add dry mixture to the wet mixture and blend until combined.
Add the Mix-Ins
Fold in chocolate chips and M&Ms.
Bake
Spread batter evenly into your 9×13 pan.
Sprinkle extra M&Ms on top.
Bake for 25–30 minutes, until edges are golden and center is set.
Cool completely before slicing.
Serve and Enjoy!
Variations
- Holiday Monster Bars: Use red & green M&Ms for Christmas (which is what I did) or pastels for Easter. You could even use pink/white/red ones for Valentine's Day, along with white chocolate chips.
- Loaded Version: Add white chocolate chips or peanut butter chips (classic version only).
- Chocolate Lover’s: Substitute ½ cup flour with cocoa powder.
- Crunchy Monster Bars: Add toffee bits or crushed pretzels.
How to Store Your Bars
- Room temp: 4–5 days in an airtight container
- Refrigerator: Up to 1 week
- Freezer: 3 months (wrap individually for best results)
Questions People Ask
Are Monster Cookies always made with peanut butter?
Yes, traditionally. But you can definitely leave out the peanut butter if you have an allergy.
Can I make these without M&Ms?
Absolutely. Replace with chocolate chips, white chocolate chips, or holiday candy.
Can I double the recipe?
Yes. Bake in a sheet pan and reduce baking time slightly.
Other Delicious Bars from Out of the Box
That's it for this post, friends!
Thanks for stopping by. Before you go, why not pin some photos to your Pinterest boards?
Monster Cookie Bars
These soft, chewy Monster Cookie Bars are packed with peanut butter, oats, chocolate chips, and colorful M&Ms. This easy recipe feeds a crowd and bakes in under 30 minutes—no scooping required!
Ingredients
- Wet Ingredients
- 1 cup (2 sticks) unsalted butter, softened
- 1 cup brown sugar, packed
- 1 cup granulated sugar
- 1 ½ cups creamy peanut butter
- 3 large eggs
- 1 tablespoon vanilla extract
- Dry Ingredients
- 2 cups quick oats
- 1 ½ cups all-purpose flour
- 1 teaspoon baking soda
- ½ teaspoon salt
- Mix-Ins
- 1 cup semi-sweet chocolate chips
- 1–1½ cups M&Ms (plus extra for topping)
Instructions
1. Preheat Oven & Prepare Pan Preheat oven to 350°F. Line a 9×13-inch pan with parchment or spray lightly with nonstick baking spray.
2. Cream Butter, Peanut Butter & Sugars In a large mixing bowl, beat together: butter brown sugar granulated sugar peanut butter Mix until smooth, fluffy, and fully combined.
3. Add Eggs & Vanilla Mix in the eggs one at a time. Add vanilla extract and blend well.
4. Combine Dry Ingredients In a separate bowl, stir together: quick oats flour baking soda salt
5. Mix Wet & Dry Add dry mixture to wet mixture and stir until combined. The dough will be thick—this is perfect.
6. Add the Mix-Ins Fold in chocolate chips and M&Ms. Reserve a handful of M&Ms for topping.
7. Press Into the Pan Spread dough evenly into your 9×13 pan. Smooth the top and sprinkle additional M&Ms across the surface for color.
8. Bake Bake for 25–30 minutes, or until: ✔ edges are golden ✔ center is set but still soft The bars will firm up as they cool.
9. Cool Completely & Slice Let bars cool at least 30–45 minutes before cutting. Cut into squares or rectangles.
Nutrition Information:
Yield: 24 Serving Size: 1Amount Per Serving: Calories: 257Total Fat: 13gSaturated Fat: 8gUnsaturated Fat: 6gCholesterol: 46mgSodium: 142mgCarbohydrates: 34gFiber: 1gSugar: 27gProtein: 3g
The nutrition information is a product of online calculators. I try to provide true and accurate information, but these numbers are estimates.
Janice Thompson is a professional baker, cake designer, and author with over 20 years of experience creating unique cakes and desserts. She’s the creator of Out of the Box Baking, where she shares her favorite doctored cake mix recipes, tutorials, and baking tips. Learn more →