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A stack of 3 monster cookie bars on a white plate.

Monster Cookie Bars

Monster Cookie Bars are everything you could want - soft, chewy, extra thick and filled with peanut butter, oatmeal, chocolate chips and M&Ms. It's an easy cookie bar recipe that's faster than making a batch of cookies and impossible to resist. 
Course Dessert
Cuisine American
Keyword Monster Cookie Bars, Monster Cookies
Prep Time 15 minutes
Cook Time 25 minutes
Total Time 45 minutes
Servings 24 squares
Calories 410kcal


  • cup butter softened
  • ¾ cup brown sugar
  • ½ cup white sugar
  • cup peanut butter
  • 1 large eggs
  • 2 teaspoons vanilla extract
  • 1 cup all-purpose flour
  • 1 teaspoon baking soda
  • ¼ teaspoon salt
  • 1 ½ cups old-fashioned oats
  • cup chocolate chips plus a few more for sprinkling on top
  • cup M&Ms plus a few more for sprinkling on top


  • Preheat the oven to 350F degrees. Line a 9x13 inch pan with parchment paper so there's a 1 to 2-inch overhang on all sides, or lightly grease. 
  • In a large bowl beat the butter, brown sugar & white sugar until combined.
  • Mix in the peanut butter, egg & vanilla extract. 
  • Turn the mixer down to low speed and mix in the flour, baking soda & salt.
  • Mix in the oats.
  • Turn off the mixer and stir in the chocolate chips and M&Ms.
  • Press the dough into the bottom of the prepared pan.
  • Bake for 22-25 minutes, or until the tops look set and around the edges is starting to brown. 
  • Cool fully (at least 30 minutes) then cut into bars. 


*Store in an airtight container at room temperature for up to 4 days. 


Calories: 410kcal