Monster Cookie Bars with chocolate frosting

Everyone needs an easy and irresistible cookie bars recipe in their back pocket, dontcha think? Because a pan of chewy Monster Cookie Bars could not be more perfect for a picnic at the park, a backyard bbq, or a neighborhood block party. They’re super quick to make (yay for you!), and are always a hit (yay for them!).

I was so happy when I got the email reply from Blake’s cousin, Melanie, and she shared her awesome recipe for these bars. When I first ate one from her pan earlier this year, there was no way I was leaving the room until I had one (or was it two?!) more.  Melanie’s monster cookie bars are perfect. They’re chewy and moist, with just the right amount of peanut butter and oats. And if the recipe looks like it calls for too much chocolate chips and M&M’s (Don’t look at me, I would never think such a thing. Ahem.), just trust me and do what the recipe says. Because all that delicious chocolate is right where it’s supposed to be.

Melanie’s bars were made with the regular colored M&M’s. But I wanted to add a little 4th of July fun to her recipe for the upcoming holiday. With a bag of holiday red, white, and blue M&M’s, plus a swirl of fudgy frosting and a scattering of patriotic sprinkles…well, I had myself a pan of eye catching cookie bars, ready for the fireworks!

a stack of Cookie Bars on a white plate

But I realize that not every occasion calls for getting out the pastry bags and tips, and that sometimes a person just wants to turn out something fabulous, without the fancy. That’s where the beauty of this recipe comes in. It’s super easy to play up the 4th of July by only incorporating the holiday M&M’s. The cookie bars are showy enough, without getting all crazy with frosting and sprinkles.

monster cookie bars

Nothing more is necessary.

Tell me…what would you make? The plain cookie bars or the fancied up ones?!

Monster Cookie Bars with chocolate frosting

Melanie’s Monster Cookie Bars {for the 4th of July!}

Yield: 48 bars
Cook Time: 15 minutes
Total Time: 15 minutes

Because a pan of chewy Monster Cookie Bars could not be more perfect for a picnic at the park, a backyard bbq, or a neighborhood block party.


  • 1/2 c. + 1 T. unsalted butter, at room temperature, divided
  • 1.5 c. creamy peanut butter
  • 1 c. packed brown sugar
  • 1 c. sugar
  • 3 large eggs
  • 1 tsp. pure vanilla extract
  • 1 c. all-purpose flour
  • 3.5 c. old fashioned oats
  • 2 tsp. baking soda
  • 1/2 tsp. kosher salt
  • 12 oz. semi-sweet chocolate chips
  • 1 12.6-oz. bag milk chocolate M&M's in red, white, and blue for July 4th, or use regular colors for other times of the year
  • fudge frosting, optional - I just used a can I picked up in the baking aisle, but this homemade chocolate ganache would also be wonderful
  • red, white, and blue sprinkles, optional


  1. Preheat oven to 350°F. Butter a 12'' x 17'' jelly roll pan with 1 tablespoon of the butter. Set aside.
  2. In the bowl of a stand mixer, cream together remaining 1/2 c. butter, peanut butter, brown sugar, and sugar. Add eggs and vanilla and mix until incorporated. Add flour, oats, baking soda, and salt, and mix again until incorporated.
  3. Then, with a spatula (and plenty of arm strength!), fold in the chocolate chips and M&M's. Press into prepared pan and bake for 14 to 15 minutes. These bars are meant to be chewy, do not over bake! Cool completely on wire rack, then cut into bars.
  4. These bars are fabulous just the way they are, but if you want to add a little more festivity for the 4th of July, try adding chocolate frosting and sprinkles! I simply used a can of fudge frosting that I picked up in the baking aisle. Place frosting in a pastry bag fitted with a medium star tip and swirl the frosting onto the top of each bar. Add some red, white, and blue sprinkles, and you're set!


Adapted from the recipe box of Blake’s cousin, Melanie Sorenson.

Nutrition Information:
Yield: 48 Serving Size: 1
Amount Per Serving: Calories: 229Total Fat: 11gSaturated Fat: 5gTrans Fat: 0gUnsaturated Fat: 5gCholesterol: 17mgSodium: 137mgCarbohydrates: 29gFiber: 2gSugar: 20gProtein: 5g

Nutrition information is automatically calculated by Nutritionix. I am not a nutritionist and cannot guarantee accuracy. If your health depends on nutrition information, please calculate again with your own favorite calculator.

Did you make this recipe?

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a white plate with a Monster Cookie Bar and m&m's

Here are a few more recipes you might like, all dressed up in red, white, and blue: