Monster Cookie Bars

Monster Cookie Bars

Stephen and I just returned from a nice little vacation in California. While we were there my brother brought us a bag of gluten free monster cookies from a local bakery. I was surprised to find out that both my mom and Stephen had never tried monster cookies. As a peanut butter, oatmeal and M&M lover, I had just assumed that everyone had tasted this delicious combination. I was wrong. I made it my goal to bake up some kind of “monster treat” when we came back home. My first thought was to do my own gluten free cookie version but since I was short on time and didn’t have the necessary ingredients, I turned to bars. Let me start off by warning you: these are not your typical monster cookie bars. Mine are ultra moist and topped with a creamy peanut butter spread that really puts them over the top! If you like your bars extra gooey, go ahead and stick to 15 minutes of baking time, they’ll be even more soft and chewy! I took these to a picnic dinner and they were a huge hit- I hope you’ll think so too!


Monster Cookie Bars Recipe

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Course: Brownies & Bars, Dessert
Cuisine: American
Prep Time: 10 mins
Cook Time: 15 mins
Cool: 30 mins
Servings: 30 bars
Calories: 280kcal
Author: Life Made Simple Team
Print Recipe


  • 2 cups all-purpose flour
  • 1 1/2 cups quick rolled oats
  • 1 cup sugar
  • 1 cup brown sugar
  • 2/3 cup peanut butter - creamy or chunky
  • 1 cup (2 sticks) butter - room temperature
  • 2 eggs
  • 1 tsp baking soda
  • 1/2 tsp salt
  • 1 tsp vanilla
  • 1/4 cup peanuts - chopped
  • 1/4 cup chocolate chips - a mix of regular and mini
  • 1/4 cup M&Ms - a mix of regular and mini
peanut butter topping
  • 2/3 cup Reese's peanut butter
  • 1 1/2 cups confectioner's sugar
  • 1/3 cup milk - more if needed
  • 1/4 tsp salt
  • 1/4 tsp vanilla
  • 1/2 cup chocolate chips - a mix of regular and mini
  • 1/2 cup M&Ms - a mix of regular and mini


  • Preheat oven to 350 degrees. Lightly grease (or cover with parchment) a full size cookie sheet with sides.
  •  In a medium size mixing bowl, whisk together oats, flour, baking soda and salt. Set aside.
  • In the bowl of a stand mixer, beat together peanut butter, butter and sugars for 1 minute. Turn speed to low and add one egg at a time. Add vanilla and mix until combined.
  • Remove bowl from stand mixer. Fold in dry ingredients, then chopped peanuts, chocolate chips and M&Ms. Pour onto prepared pan and pat down until even. I like to use a my hands to get it all spread out, and then a spatula to make it smooth and even. Place in oven and bake for 15-18 minutes, or until the top begins to brown. 
  • While the bars are baking, in a medium size mixing bowl, combine all of the topping ingredients. Using a hand mixer, beat until smooth (it should be a spreadable consistency, but will it will also melt and get shiny on contact). Set aside until needed.
  • Remove bars from oven and place pan on a wire rack. Allow to cool for 8 minutes before spreading the peanut butter topping over the entire sheet. It should become smooth and melty, spread until even. Sprinkle remaining chocolate chips and M&Ms over top, allow to cool for 30-40 more minutes before cutting into bars.


Calories: 280kcal | Carbohydrates: 38g | Protein: 6g | Fat: 15g | Saturated Fat: 7g | Polyunsaturated Fat: 2g | Monounsaturated Fat: 5g | Trans Fat: 1g | Cholesterol: 29mg | Sodium: 215mg | Potassium: 126mg | Fiber: 2g | Sugar: 21g | Vitamin A: 228IU | Vitamin C: 1mg | Calcium: 32mg | Iron: 1mg

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  1. Monster cookies are my favorite! Love that you topped the bars with even more peanut butter!

  2. Help! I’m making these now and I’m confused (as usual). For the topping, is it the Reeses peanut butter CHIPS or peanut butter (I’m thinking peanut butter but I’ve never seen Reeses peanut butter). Can you help me — fast!!! ha ha

    1. Never mind – I sort of figured it out since the chips wouldn’t be smooth!! Duh — I bet you hate dumb bakers like me!! But I LOVE you and your awesome recipes. Thanks you.

    2. Sorry about that- yes, it’s just peanut butter 🙂 Thanks for giving these a try!