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Monster cookie bars are a fun treat loaded with peanut butter, oats, chocolate chips, peanut butter chips, and mini m&m's. They bake up perfectly soft, chewy, and thick. A fun treat to make with the kids or great for back-to-school lunches or after school treat. 

Soft-Baked Monster Cookie Bars

Monster Cookie Bars loaded with peanut butter, oats, chocolate chips, peanut butter chips, and mini m&m's. They bake up perfectly soft, chewy, and thick.
Course Dessert
Cuisine American
Keyword monster cookie bars
Prep Time 10 minutes
Cook Time 15 minutes
Total Time 25 minutes
Servings 20 bars
Calories 245kcal
Author Jessica


  • cups all-purpose flour
  • ¾ teaspoon baking soda
  • ¼ teaspoon salt
  • 1 cup quick oats
  • 1/2 cup butter softened
  • 1/3 cup creamy peanut butter not all natural
  • 1/2 cup granulated sugar
  • 1/2 cup light brown sugar
  • 1 teaspoon vanilla extract
  • 1 large egg
  • 1 large egg yolk (discard the whites, only use the yolk)
  • 1/2 cup peanut butter chips
  • 1/2 cup miniature semi-sweet chocolate chips
  • 1/2 cup mini m&m's


  • Preheat the oven to 350 degrees. Lightly grease a 9X13-inch baking pan, or line with parchment paper or tin foil. Set aside.
  • In a small bowl, whisk together the flour, baking soda, salt and oats. Set aside until later.
  • In a separate large bowl, or in the bowl of a stand mixer fitted with the paddle attachment, cream together the butter, peanut butter, brown sugar, and sugar until fluffy looking and light in color, about 2 minutes.
  • Add in the vanilla, egg and egg yolk. Blend together well.
  • Add the dry ingredients, peanut butter chips, chocolate chips, and mini m&m's into the wet mixture and beat on low speed just until combined.
  • Press the dough into the prepared pan. Bake for 13½-18 minutes or until very lightly browned on the edges. The bars will still look pale and slightly underdone in the middle. That's ok. Don't over bake or the bars will be dry!
  • Let the bars cool in the baking pan for 20-30 minutes. Cut into squares.


For a pretty presentation gently press some additional m&m's and chocolate chips onto the top of the bars before baking. 
I always bake with salted butter. If you are using unsalted butter then increase the salt to 1/2 teaspoon. 
All-natural peanut butter is drier and does not have the oil and fat content of regular peanut butter which is why it's best to not use all-natural peanut butter when baking. It tends to dry out baked goods. 
When I bake these they are done at 13 minutes but I know some people have said their bars cook for longer, like closer to 15 minutes. Just be sure that you are not over baking the bars. They are much better even when they're slightly under baked because then at least they are soft and thick instead of dry and crumbly. 


Calories: 245kcal | Carbohydrates: 30g | Protein: 5g | Fat: 12g | Saturated Fat: 7g | Cholesterol: 33mg | Sodium: 149mg | Potassium: 97mg | Fiber: 2g | Sugar: 18g | Vitamin A: 182IU | Calcium: 23mg | Iron: 1mg