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These Thick & Chewy Monster Cookie Bars taste just like your favorite monster cookie recipe but EASIER! Loaded with chewy oats, creamy peanut butter, gooey chocolate chips and crunchy mini M&M's, they're flavorful, thick, super chewy, and DELICIOUS!
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5 from 2 votes

Thick & Chewy Monster Cookie Bars

These Monster Cookie Bars are supremely thick, chewy, hearty, and packed with amazing flavor from peanut butter, chocolate, and miniature M&M's candies! A must-try, and so much easier than making drop cookies!
Prep Time10 mins
Cook Time30 mins
Total Time40 mins
Course: Bars, Cookies, Dessert
Cuisine: American, Dessert
Servings: 15 -18
Author: Hayley Parker, The Domestic Rebel


  • 3/4 cup unsalted butter softened
  • 2 cups brown sugar
  • 3/4 cup creamy peanut butter
  • 2 large eggs
  • 1 Tbsp vanilla extract
  • 1 tsp baking powder
  • 1/4 tsp baking soda
  • 1/4 tsp kosher salt
  • cups all-purpose flour
  • cups old-fashioned oats not quick oats
  • 3/4 cup chocolate chips
  • 1 cup miniature M&M's candies


  • Preheat oven to 350 degrees F. Line a 13x9" rectangular baking pan with foil, extending the sides of the foil over the edges of the pan. Spray the foil liberally with cooking spray; set aside.
  • In the bowl of a stand mixer, cream together the butter and brown sugar until smooth and fluffy, about 1 minute. Beat in the peanut butter, followed by the eggs and vanilla. Add in the baking powder, baking soda, salt, and flour and mix on low-speed until just barely combined. Beat in the oats, chocolate chips, and M&M's candies until just combined.
  • Press the dough into the prepared baking pan evenly and bake for approximately 20-30 minutes or until the top is golden brown and set. Cool in the pan completely before cutting into bars.