A stack of two No Flour Monster Cookie Bars on a small white plate

Monster Cookie Bars

A fully-loaded bar cookie you can make in one bowl in no time. Crisp on the outside, chewy on the inside, and filled with peanut butter, oats, chocolate chips, and M&M's.
Course Dessert
Cuisine American
Keyword Cookie Bar Recipe, Monster Cookie Bars, No Flour
Prep Time 15 minutes
Cook Time 16 minutes
Servings 9 bars
Calories 449.01kcal
Author Brianne @ Cupcakes & Kale Chips


  • 3 Tablespoons butter, softened
  • 3/4 cup light brown sugar
  • 1/3 cup white sugar
  • 1 egg
  • 1 egg yolk
  • 1 teaspoon vanilla extract
  • 1 Tablespoon maple syrup
  • 1/2 teaspoon baking soda
  • 2/3 cup crunchy peanut butter
  • 2 cups old-fashioned rolled oats, certified gluten free if needed
  • 1/3-1/2 cup semi-sweet chocolate chips
  • 1/4-1/2 cup M&M's candies for topping


  • Preheat the oven to 350°F. Line an 8-inch square pan with parchment paper or grease well with butter.
  • Combine the butter, brown sugar, and white sugar in a large bowl and beat to combine. Add the egg, egg yolk, vanilla, syrup, and baking soda. Stir in the peanut butter. Add the oats and stir until well combined. Mix in the chocolate chips.
  • Press the dough into the bottom of the prepared pan. Top with the M&M's and lightly press them into the dough. Bake 16 to 17 minutes, or until the bars are lightly browned and just past looking wet on top. They will not be firm, but they will set up as they cool. Let it cool completely before slicing. Store in an airtight container.


  • While it says you can butter your pan well, lining the pan with parchment paper is definitely recommended. Let the parchment overhang the edges by at least an inch, then use the edges to pull the entire thing out at once. This makes it easier to slice the cooled bars on a cutting board.
  • The recipe calls for salted butter. If you only have unsalted butter, just add a pinch of salt.
  • When measuring peanut butter, grease your measuring cup with butter or cooking spray so it slides out easily.
  • Let them cool for at least 15 minutes. There will be some carryover cooking, they will be easier to cut, and you definitely want to store fully cooled bars.
  • Baking for someone avoiding gluten? These are perfect because they are flourless, but if you are dealing with celiac or an allergy, make sure your oats are certified gluten free.
  • Once you have mastered the basic version, try switching it up with different nut butters and candy mix-ins.


Serving: 1bar | Calories: 449.01kcal | Carbohydrates: 56.12g | Protein: 9.32g | Fat: 22.11g | Saturated Fat: 8.82g | Cholesterol: 52.25mg | Sodium: 205.13mg | Potassium: 282.02mg | Fiber: 4.08g | Sugar: 39.44g | Vitamin A: 197.74IU | Calcium: 61.26mg | Iron: 2.17mg