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A batch of monster cookie bars topped with colorful candy-coated chocolates, cut into squares on parchment paper, with a large knife next to them on a wooden surface.
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Monster Cookie Bars

These easy Monster Cookie Bars combine creamy peanut butter, old-fashioned oats, chocolate chips, and colorful M&Ms in one delicious sheet pan dessert. Naturally gluten-free and perfect for feeding a crowd!
Prep Time15 minutes
Cook Time22 minutes
Total Time37 minutes
Course: Dessert
Cuisine: American
Diet: Gluten Free
Servings: 32 bars
Author: Melissa Griffiths

Ingredients

  • ¾ cup granulated sugar
  • ⅓ cup brown sugar packed
  • ¼ cup butter softened
  • 1 cup creamy peanut butter or chunky if you prefer
  • 1 large egg
  • 2 teaspoons vanilla extract
  • 1 teaspoon baking soda
  • ½ teaspoon salt
  • 3 cups old-fashioned oats
  • 1 cup M&M candies (I prefer mini M&M's.)
  • 1 cup chocolate chips

Instructions

  • Preheat the oven to 350°F (175°C). Grease a 9x13-inch baking dish and set aside. You can also line the baking dish with parchment paper if you'd like to remove the bars for serving.
  • In a large bowl, beat together the granulated sugar, brown sugar, softened butter, and peanut butter until smooth and creamy. Add the egg and vanilla, and mix until well combined.
  • Stir in the baking soda and salt, then mix in the oats until evenly distributed. Fold in the M&M’s and chocolate chips. I like to leave 1/3 of the M&M's out of the batter and save them to press on the top.
  • Press the dough firmly and evenly into the prepared baking dish. Sprinkle on extra M&M's if you saved them and press them in firmly into the top.
  • Bake for 22–26 minutes, or until the edges are golden brown and the center is set.
  • Let cool in the pan before slicing into bars. Enjoy!

Notes

Gluten-Free Treat: I LOVE that these are naturally gluten free, so keep that in the you back pocket for when you need to host your GF girlies! Be sure to use gluten free oats if that's your goal.
Oat Choices: You can use old fashioned or instant oats or a combo of the two. The texture just changes a little bit depending on the oat you use. 
Switch Up Add-Ins: You can do all kinds of fun things with the M&M's and chocolate chips. Use different kinds of M&M's and chocolate chips to make this your own. Try a mix of peanut butter chocolate chips, normal chocolate chips, and peanut butter M&M's. And it's especially fun to coordinate the add-ins with the current season or holiday with colored or specially flavored chips and candies. SO good!
Good At All Temps: These firm up nicely when cooled and are soft and gooey when warm. I recommend eating them at all of the stages!

Nutrition

Serving: 1bar | Calories: 180kcal | Carbohydrates: 22g | Protein: 3g | Fat: 9g | Saturated Fat: 4g | Polyunsaturated Fat: 1g | Monounsaturated Fat: 3g | Trans Fat: 0.1g | Cholesterol: 10mg | Sodium: 124mg | Potassium: 95mg | Fiber: 1g | Sugar: 15g | Vitamin A: 66IU | Vitamin C: 0.04mg | Calcium: 23mg | Iron: 1mg

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