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Monster Cookie Bars

Monster cookie bars are the perfect dessert for parties or a sweet treat. Chewy peanut butter oatmeal bars are stuffed with chocolate chips and M&M’s!

monster cookie bars cut into pieces

Monster cookie bars are a classic dessert that is filled to the brim with sweet chocolate chips and colorful M&M’s. It’s the perfect sweet treat for weekend baking, parties, graduations, bake sale, potlucks, and more!

My kids love these chewy peanut butter oatmeal bars so much that it has inspired us to created recipes like monster cookie energy balls and gluten free monster cookies.

These bars are packed full of so many yummy flavors and are sure to be a hit no matter what occasion you are baking for.

monster cookie bars stacked between pieces of parchment paper
  • butter
  • brown sugar
  • sugar
  • no stir creamy peanut butter
  • eggs
  • oats: you will need classic rolled oats
  • all purpose flour
  • vanilla extract
  • M&M’s: try making these using seasonal M&M’s for a holiday themed treat!
  • semi sweet chocolate chips
  • baking soda
  • salt
ingredients needed to make monster cookie bars

How to make monster cookie bars

Step 1: Whisk together the dry ingredients in a bowl: rolled oats, all purpose flour, baking soda, and salt.

oats, flour, salt, and baking soda


Step 2: In a separate bowl, cream together the butter, peanut butter, sugar and brown sugar until smooth

adding the butter and sugars to a bowl

Add the eggs and vanilla extract and beat to combine.

adding the eggs and vanilla extract to the batter

Step 3: Add the dry ingredients to the wet and mix to combine.

wet ingredients, dry ingredients, chocolate chips, and M&M's

Step 4: Fold in ¾ cup of chocolate chips and ½ cup of M&M’s.

Tip: Try making these holiday themed! Use Valentine’s M&M’s, or red and green for a Christmas themed monster cookie bar!

adding the chocolate chips and M&M's to the batter

Step 5: Spray the bottom of a 9 by 13 baking dish, then line it with parchment paper to overhang the sides (this will make it easier to get the bars out).

Use a rubber spatula to press the monster cookie batter into the lined baking dish. Top with additional M&M’s.

Bake the monster cookie bars at 350 degrees for 23 – 27 minutes, until very lightly browned on the edges. Remove and allow to cool completely (or at least one hour). The bars will continue to cook so be careful not to over bake them.

Step 6: Once the bars have cooled completely, use the parchment paper edges to lift the bars from the pan. Cut into pieces and serve!

You can either cut these bars into 12 large pieces, or 18+ smaller ones. If you are making these for a bake sale or party, I would cut them into 24 pieces as they will still be plenty big enough.

monster cookie bars cut into pieces

How to store

Once the baked bars have completely cooled, store them in an airtight container. They will last several days at room temperature.

If you have any leftovers, these will also keep well in the freezer for a month or two. Just store them in an airtight bag or freezer safe container.

monster cookie bars stacked between pieces of parchment paper

More Cookie Bars

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monster cookie bar propped up on a glass of milk

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monster cookie bars cut into pieces

These are the perfect dessert to make for family and friends. No matter what the occasion, these easy monster cookie bars are sure to be a hit with anyone who tries them!

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Yield: 18 bars

Monster Cookie Bars

monster cookie bars cute into pieces

Monster Cookie Bars are the best dessert! Chewy peanut butter oatmeal cookie bars mixed with chocolate chips and M&M's.

Prep Time 15 minutes
Cook Time 25 minutes
Total Time 40 minutes

Ingredients

  • ½ cup salted butter, melted
  • 1 cup brown sugar
  • ½ cup sugar
  • 1 ½ cups no stir creamy peanut butter
  • 3 eggs
  • 2 cups rolled oats
  • 1 ½ cups all purpose flour
  • 1 tablespoon vanilla extract
  • ½ cup M&M’s, plus more for topping
  • ¾ cup semi sweet chocolate chips
  • 1 teaspoon baking soda
  • 1 teaspoon salt

Instructions

  1. Whisk together the oats, flour, baking soda, and salt
  2. In a separate bowl, cream together the butter, peanut butter, sugar and brown sugar until smooth. Add the eggs and vanilla extract and beat to combine
  3. Add the dry ingredients to the wet and mix to combine
  4. Fold in ¾ cup of chocolate chips and ½ cup of M&M’s
  5. Spray the bottom of a 9 by 13 baking dish, then line it with parchment paper to overhang the sides (this will make it easier to get the bars out)
  6. Use a rubber spatula to press the monster cookie batter into the lined baking dish
  7. Top with additional M&M's
  8. Bake at 350 degrees for 23 - 27 minutes, until very lightly browned on the edges. Remove and allow to cool completely (or at least one hour). The bars will continue to cook in the pan so be careful not to over bake them. 
  9. Once the bars have cooled, remove them from the baking dish and cut into 12 large pieces, or 18 smaller bars
  10. Store leftover bars in an airtight container

Nutrition Information:

Yield:

18

Serving Size:

1

Amount Per Serving: Calories: 381Total Fat: 21gSaturated Fat: 8gTrans Fat: 0gUnsaturated Fat: 10gCholesterol: 45mgSodium: 350mgCarbohydrates: 44gFiber: 3gSugar: 25gProtein: 9g

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