Monster Cookie Bars

Bake a big batch in a flash.

By
Kalisa Marie Levette
Kalisa Marie Martin
Kalisa Marie Levette
Kalisa Marie Martin a is classically trained chef, content creator, and travel entrepreneur of Jamaican heritage.
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Updated August 29, 2024
Kalisa Marie Martin
Close up of an overhead view of Bar Cookies of the Gluten Free Monster Variety.
Kalisa Marie Martin

Ever heard of monster cookies? To know them is to love them.

If you are familiar, you likely have connections to the Midwest, where they’re a favorite. Imagine oatmeal peanut butter cookies studded with chocolate chips and M&Ms. Once you try them, you’ll agree that they should be making them in all 50 states!

Scooping, shaping, and baking cookies in batches takes time and effort. If you spread your entire bowl of cookie dough out on a sheet pan instead, you can get the job done in one go. Then, all you have to do is cut them into squares after they’ve baked.

Not only is this recipe a breeze for the baker, but it is a dream for whoever gets to eat them. These cookies are soft, chocolatey, and nutty! The oats add a great chewiness, the chocolate chips add to the melty gooey texture, and the M&Ms maintain their shape and crunch.

Roll with Your Jelly Roll Pan

For sheet pan cookies, we need to use a pan with higher edges that will contain the cookie dough as it rises in the oven and a jelly roll pan is perfect for this. A jelly roll pan is smaller than a half-sheet pan; 15x10 inches in size and has 1-inch higher sides so there won’t be any overflow of dough as it bakes in the oven.

Gluten-Free Sheet Pan Monster Cookies stacked on a plate.
Kalisa Marie Martin.

Mix and Match Monster Cookie Bars

There’s more than one way to make a monster cookie and you can take this recipe and make it your own. Just be sure that the mix-ins stay around 2 cups total.

  • Try half M&Ms and half Reese’s Pieces.
  • Throw in some chopped peanuts!
  • If you have a peanut allergy swap peanut butter for almond butter or even sunflower seed butter to avoid nuts all together. (But stick to creamy versus crunchy and avoid any brands that are 100% natural. Natural nut butters will actually lead to a drier cookie.)
  • Try crushed pretzels or potato chips.

 Quick or Rolled Oats?

The BEST GF Monster Cookie Recipe sliced into squares and set on parchment paper.
Kalisa Marie Martin

This recipe calls for quick oats, as the finer texture helps to bind the cookie dough together. If you only have old fashioned oats, pulse them a few times in a food processor to break them down. Your cookies will have a crumbly texture if you use old fashioned oats without pulsing them first.

Raising the Bar for Bar Cookies

Monster Cookie Bars

Prep Time 15 mins
Cook Time 15 mins
Total Time 30 mins
Servings 24 cookie squares

If baking gluten-free, use your favorite all-purpose gluten-free flour blend and be sure to use gluten-free oats (which are processed in a facility that's free of gluten).

This recipe calls for quick oats, as the finer texture helps to bind the cookie dough together. If you only have old fashioned oats, pulse them a few times in a food processor to break them down. Your cookies may have a crumbly texture if you use old fashioned oats without pulsing them first.

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Ingredients

  • 1 cup all-purpose flour (if baking gluten-free, use gluten-free flour such as King Arthur Measure for Measure)

  • 1 cup quick oats (regular quick oats will work if you are not baking these gluten-free)


  • 1/2 teaspoon salt

  • 1/2 teaspoon baking soda

  • 1/2 cup unsalted butter, melted and cooled

  • 1 cup light brown sugar, packed

  • 1/2 cup creamy peanut butter

  • 1 large egg

  • 1 teaspoon vanilla extract

  • 1 cup M&Ms, divided

  • 1 cup chocolate chips

Method

  1. Preheat the oven and prepare the baking pan:

    Preheat the oven to 350°F. Line the jelly roll pan with parchment paper leaving a 1-inch overhang on the two long sides. You will use this later to lift the bars out of the pan.

    Lining a pan with parchment to make Bar Cookies of the Gluten Free Monster Variety
    Kalisa Marie Martin
  2. Combine the dry ingredients:

    In a medium bowl, whisk together gluten-free flour, gluten-free oats, salt, and baking soda.

    Adding flour to a bowl to make Bar Cookies of the Gluten Free Monster Variety.
    Kalisa Marie Martin
    Whisking dry ingredients in a bowl to make Gluten-Free Sheet Pan Monster Cookies.
    Kalisa Marie Martin
  3. Combine the wet ingredients:

    In a separate large bowl, whisk together the butter, brown sugar, peanut butter, egg, and vanilla until completely smooth.

    Whisking sugars and egg in a bowl to make Gluten-Free Sheet Pan Monster Cookies.
    Kalisa Marie Martin
    Whisking sugars and egg in a bowl to make Gluten-Free Sheet Pan Monster Cookies.
    Kalisa Marie Martin
  4. Combine the wet and dry ingredients:

    Add the dry ingredients to the bowl of wet ingredients and stir to combine. Reserve 2 tablespoons each of the M&Ms and chocolate chips. Add the remainder to the cookie dough and stir to combine

    Adding flour mixture to wet mixture to make Gluten-Free Sheet Pan Monster Cookies.
    Kalisa Marie Martin
    Adding flour mixture to wet mixture to make Gluten-Free Sheet Pan Monster Cookies.
    Kalisa Marie Martin
  5. Transfer dough to prepared baking pan:

    Turn the dough out onto the prepared baking pan. Place a sheet of parchment paper on top and use your hands to gently press it evenly into the pan. Remove the top piece of parchment. Sprinkle the reserved M&Ms and chocolate chips on top, pressing them just slightly into the dough

    Dough for The BEST GF Monster Cookie Recipe in a baking pan.
    Kalisa Marie Martin
    Pressing dough with parchment paper with hands to make Gluten-Free Sheet Pan Monster Cookies.
    Kalisa Marie Martin
    Gluten-Free Sheet Pan Monster Cookies ready to be baked.
    Kalisa Marie Martin
  6. Bake cookie bars:

    Bake the cookie bars until the dough has risen and the edges have just begun to turn slightly golden, 15 to 17 minutes. The middle may appear under done, but it will set as it cools.

    Gluten-Free Sheet Pan Monster Cookies baked in pan.
    Kalisa Marie Martin
  7. Cool the cookie bars:

    Cool in the baking pan on a cooling rack for at least 1 hour.

  8. Cut and serve the cookie bars:

    Using the sides of the parchment as a sling, transfer the sheet pan cookie to a board and cut into 24 bars and serve.

    Store in an airtight container at room temperature. They will stay chewy for about 5 days. You can also freeze them between layers of parchment and sealed in a zip-top bag for up to 3 months.

    Removing Gluten-Free Sheet Pan Monster Cookies from the pan by holding the parchment.
    Kalisa Marie Martin
    Sliced Gluten-Free Sheet Pan Monster Cookies.
    Kalisa Marie Martin
Nutrition Facts (per serving)
207 Calories
11g Fat
26g Carbs
3g Protein
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Nutrition Facts
Servings: 24
Amount per serving
Calories 207
% Daily Value*
Total Fat 11g 14%
Saturated Fat 5g 27%
Cholesterol 19mg 6%
Sodium 108mg 5%
Total Carbohydrate 26g 9%
Dietary Fiber 1g 5%
Total Sugars 17g
Protein 3g
Vitamin C 0mg 0%
Calcium 26mg 2%
Iron 1mg 5%
Potassium 113mg 2%
*The % Daily Value (DV) tells you how much a nutrient in a food serving contributes to a daily diet. 2,000 calories a day is used for general nutrition advice.
Nutrition information is calculated using an ingredient database and should be considered an estimate. In cases where multiple ingredient alternatives are given, the first listed is calculated for nutrition. Garnishes and optional ingredients are not included.