Sheet Pan Monster Cookie Bars (Flourless/Gluten Free)

These big batch monster cookie bars are loaded with M&Ms, chocolate chunks and peanut butter! I recently made these bars for my friends at church and they were a hit with the kids because of the colorful M&Ms tucked inside, not to mention, there were hardly any leftovers.

These bars are made without flour, making them gluten free and perfect for serving a crowd. These cookie bars stay soft for several days, but also have a nice and chewy texture from the rolled oats. If you love to whip up a batch of bars for your family or friends, be sure to check below the recipe card for a list of our favorites!

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Big batch monster cookie bars flourless

Sheet Pan Monster Cookie Bars

marilynpeight
These flourless, big batch monster cookie bars are popular with kids and adults alike! The tasty combination of peanut butter, chocolate chunks, M&Ms and oats makes a "monstrously" good bar, perfect for serving friends and family, or for freezing to put into lunches.
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Prep Time 15 minutes
Cook Time 20 minutes
Course Dessert
Cuisine American
Servings 30 bars

Equipment

  • 12 by 17 inch sheet pan (linked below)
  • Mixing bowl (linked below)
  • Stainless steel measuring cups (linked below)
  • Mixing spoon (linked below)

Ingredients
  

  • 1/2 cup butter softened
  • 1 cup brown sugar
  • 1 cup granulated sugar
  • 3 large eggs
  • 1 3/4 cups creamy peanut butter
  • 2 teaspoons baking soda
  • 4 1/2 cups rolled oats (leveled) *see note
  • 4 oz. chocolate bar of your choice, roughly chopped I prefer to use Hershey's chocolate bars
  • 1 cup M&Ms

Instructions
 

Preheat oven to 350:

  • In a large mixing bowl, cream butter and sugars together. Add eggs and peanut butter, then mix well until the mixture is fluffy and well incorporated. Mix in the baking soda, then fold in the oats, M&Ms and chocolate chunks.
  • Line a 12 by 17 inch baking sheet (with sides) with parchment paper. Spread the cookie dough evenly into the baking sheet using a spatula. Bake the bars in the preheated oven for 15-20 minutes until golden on top and set in the center.
  • Optional: press additional M&Ms and chocolate chunks onto the top of the warm cookie bars, then allow the bars to cool before cutting and serving. Enjoy! Storage notes below.

Notes

If making this recipe for those with Gluten sensitivities, be sure to use rolled oats that are labeled “Gluten free” on the packaging. 
Additional notes and step by step photos below. 
Keyword Monster cookie bars, big batch, gluten free, sheetpan, rolled oats
Tried this recipe?Let us know how it was!

Equipment needed for these flourless Monster Cookie Bars:

  • Sheet pan for the amount of bars this recipe produces, you will need a 12 by 17 inch baking sheet with sides, or 2, 13 by 9 inch baking dishes. For easier removal of the cookie bars, be sure to line the baking sheet/baking dishes with parchment paper.
  • Mixing bowl I like to use a stainless steel mixing bowl for mixing up the cookie dough. Stainless steel bowls are easier to clean than plastic bowls, plus they are dish washer friendly!
  • Measuring cups I also prefer to use stainless steel measuring cups for measuring out the ingredients needed for these monster cookie bars.
  • Mixing spoon A large mixing spoon is useful for mixing up the cookie dough. You will also need a whisk for the wet ingredients and a spatula for spreading the dough into the baking sheet.

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Other fun and easy cookie bar recipes you may enjoy:

Ingredients needed for these Monster Cookie Bars: butter, peanut butter, brown sugar, granulated sugar, old fashioned rolled oats (be sure to use a brand labeled gluten free if gluten sensitive), eggs, M&Ms and chocolate chunks.

Additional add-in ideas:

Hershey’s chocolate bars are not the only chocolate you can add to these monster cookie bars. You can also add chocolate chips, dark chocolate, white chocolate, or your favorite candy bar that has been chunked into smaller pieces. You may even enjoy a mixture of Reese’s peanut butter pieces with or instead of the M&Ms.

Step 1: In a medium sized bowl, cream butter and sugars together. Add eggs and peanut butter, then mix well until the mixture is fluffy and well incorporated. Mix in the baking soda, then fold in the oats, M&Ms and chocolate chunks.

Step 2: Line a 12 by 17 inch baking sheet (with sides) with parchment paper. Spread the cookie dough evenly into the baking sheet using a spatula. Bake the bars in the preheated oven for 15-20 minutes until golden on top and set in the center.

Step 3: Optional: press additional M&Ms and chocolate chunks onto the top of the warm cookie bars, then allow the bars to cool before cutting and serving. Enjoy!

Storage options and prep ahead tips:

Because these monster cookie bars come in a batch of 2.5-3 dozen (depending on how big you cut them), you may wish to freeze some for later or give some to friends. These cookie bars keep well at room temperature for several days without losing too much of their soft texture. If you wish to keep the bars fresh for even longer than several days, you can freeze them for up to three months. If freezing these bars for lunches, you can wrap them individually before freezing, or simply freeze them in an airtight container.

Feel free to pin this recipe for later and don’t forget to tag me on Instagram to show off a photo of your own creation of this recipe. Thank you for your support!

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