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Monster cookie bars are jam packed with layers, textures, and flavors. The chewy oat crust and smooth chocolate are the perfect pair.

These bars are called monster because they are a monster of a cookie! Just huge, and gooey, and so extremely delicious. For more cookie musts try the cookie form of this treat: Monster Cookies, or some other fan favorites: Chocolate Chip Cookie Bars and Giant M&M Cookies.

Monster cookie bars stacked on top of each other
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Monster Cookies for a Crowd

These ooey gooey monster cookie are bars are PACKED with chocolatey goodness!

The oat-filled crust is crunchy and the perfect base for all of the flavor layers. The combination of melted chocolate and M&Ms give a great contrast – perfect for the oats and chocolate lover!

They are perfect to fulfill that sweet tooth craving, and because you make a pan full they are a great dessert for crowds.

We love to whip these up when we have visitors, or if we want to deliver a special treat to a special someone.

You will love how easy they are to make, my girls love to make them on their own. They feel so proud when they can make a recipe without help. Enjoy these bars together soon, you won’t regret it!

The oat layer of monster cookie bars in a glass baking dish

Tips for Making Them

PREP. Preheat the oven to 350 degrees F and grease a 9×13 inch baking pan.

ADD. Add the oats, flour, brown sugar, salt, softened butter, and 1/4 c peanut butter to a medium size bowl and stir together with a spoon.

MIX & PRESS. Once the ingredients have been combined remove 1 cup and set it aside. Add the remaining mixture from the mixing bowl to the greased baking pan and press.

MELT. Add the condensed milk, chocolate chips and 1/4 c of peanut butter to a saucepan and melt over medium-low heat. Stir constantly until the chocolate has melted and all the ingredients have incorporated together.

POUR. Pour the melted chocolate mixture on top of the mixture that was pressed into the baking pan, Use a cooking spatula to spread it evenly.

SPRINKLE. Take the 1 cup of the oat mixture that you set aside earlier and sprinkle it evenly over the top of the chocolate layer.

BAKE & SERVE. Top with M&M’s and bake for 25-27 minutes. Once done allow the cookie bars to cool completely before cutting them.

Variations

For me this recipe is perfect as is, but I know that sometimes it’s fun to be able to change things up so I like to give ideas that I think I may try, or that others would like. Here are some easy variations:

  • Use crunchy peanut butter for added nutty texture.
  • Top with Reese’s pieces for more peanut buttery taste.
  • Sprinkle chocolate or white chocolate chips to the top.
  • Use dark brown sugar for a hint of a carmely flavor. The extra molasses may also give a slightly chewy texture.
  • Add toffee bits.
Monster cookie bar recipe in a glass baking dish

Storage Tips

STORE the bars covered tightly with plastic wrap. They should last at room temperature for 3-4 days.

You can also FREEZE the bars for later. I like to cut them before freezing. I’ll wrap each bar with plastic wrap and store them together in a Ziploc.

They’ll easily last in the freezer for 1-2 months.

A stack of monster cookie bars
5 from 9 votes

Monster Cookie Bars Recipe

By: Lil’ Luna
Monster cookie bars are jam packed with layers, textures, and flavors. The chewy oat crust and smooth chocolate are the perfect pair.
Servings: 20
Prep: 10 minutes
Cook: 25 minutes
Total: 35 minutes

Ingredients 

  • 1 1/2 c quick oats
  • 1 1/2 c all-purpose flour
  • 1 c brown sugar
  • 1 tsp salt
  • 3/4 c butter softened
  • 1/4 c creamy peanut butter
  • 14 oz sweetened condensed milk
  • 1 bag milk chocolate chips
  • 1/4 c creamy peanut butter
  • 1 c M&M's

Instructions 

  • Preheat the oven to 350 degrees F and grease a 9×13 inch baking pan.
  • Add the oats, flour, brown sugar, salt, softened butter, and 1/4 c peanut butter to a medium size bowl and stir together with a spoon.
  • Once the ingredients have been combined remove 1 cup and set it aside. Add the remaining mixture from the mixing bowl to the greased baking pan and press.
  • Add the condensed milk, chocolate chips and 1/4 c of peanut butter to a saucepan and melt over medium-low heat. Stir constantly until the chocolate has melted and all the ingredients have incorporated together.
  • Pour the melted chocolate mixture on top of the mixture that was pressed into the baking pan, Use a cooking spatula to spread it evenly.
  • Take the 1 cup of the oat mixture that you set aside earlier and sprinkle it evenly over the top of the chocolate layer.
  • Top with M&M's and bake for 25-27 minutes. Once done allow the cookie bars to cool completely before cutting them.

Nutrition

Calories: 398kcal, Carbohydrates: 53g, Protein: 6g, Fat: 19g, Saturated Fat: 10g, Cholesterol: 29mg, Sodium: 254mg, Potassium: 164mg, Fiber: 2g, Sugar: 39g, Vitamin A: 327IU, Vitamin C: 1mg, Calcium: 106mg, Iron: 1mg

Nutrition information is automatically calculated, so should only be used as an approximation.

About Kristyn

My name is Kristyn and I’m the mom of SIX stinkin’ cute kids and the wife to my smokin’ hot hubby, Lo. My mom’s maiden name is Luna, and I’m one of the many crafty “Lil’ Lunas” in the fam. On this site I like to share all things creative - from recipes to home decor to gifts and home decor ideas. Welcome!

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5 from 9 votes (3 ratings without comment)

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Recipe Rating




6 Comments

  1. Jen says:

    5 stars
    The hardest thing about making these is adding the M&Ms before my kids try and eat them all. A family favorite!

  2. Betsy Carney says:

    5 stars
    These are my kids favorite! We make them all the time!

  3. Matt says:

    5 stars
    I LOVE monster cookies. I haven’t tried them in bar form. I can’t wait to make this recipe. 🙂

  4. Kristina says:

    5 stars
    I love being able to wrap and freeze these for my kids lunches. It’s a Delicious and fun treat.

  5. Joy says:

    5 stars
    One of my go-to desserts, because they are super easy to make & everyone loves them!

  6. Olivia says:

    5 stars
    A dessert that easily feeds a crowd filled with all kinds of goodies.