Go Back
+ servings
stack of monster cookie bars
Print Recipe
No ratings yet

Monster Cookie Bars

Monster Cookie Bars - this easy bar cookie recipe is full of peanut butter, oats, and tons of M&Ms! EVERYONE loves these, especially with ice cream!
Prep Time15 minutes
Cook Time30 minutes
Total Time45 minutes
Course: Dessert
Cuisine: American
Servings: 24 bars
Calories: 322kcal
Author: Dorothy Kern
Cost: $8


  • ½ cup (113 g) unsalted butter softened
  • 1 cup (268 g) peanut butter
  • ¾ cup (150g) packed brown sugar
  • ½ cup (100g) granulated sugar
  • 2 large eggs
  • 1 teaspoon vanilla extract
  • ½ teaspoon baking soda
  • ½ teaspoon salt
  • ¾ cup (93g) all-purpose flour
  • 3 cups (240g) quick cooking oats
  • 1 cup (170g) chocolate chips
  • 2 cups M&Ms any kind, I used regular and peanut butter


  • Preheat oven to 350°F. Line a 9x13” pan with foil and spray with nonstick cooking spray.
  • Beat butter and peanut butter with a hand or a stand mixer until smooth. Mix in both sugars until creamy. Add eggs, vanilla, baking soda, and salt and mix until smooth, then slowly mix in the flour and oats. Stir in the chocolate chips and M&Ms.
  • Press cookie dough into the prepared pan. If desired, sprinkle more M&Ms on top for decoration. Bake for 22-25 minutes or just until the edges are golden brown. Cool before cutting into bars.
  • These are great served as bars or as an ice cream sundae! Store in an airtight container for up to 3 days or freeze for up to one month.



  • Make Christmas Monster Cookie Bars with holiday M&Ms
  • Reese's Pieces Monster Cookie Bars would be fantastic - just swap the M&Ms for Reese's Pieces!
  • Do not over bake these - they're best a little under baked and gooey
  • How to serve Monster Bars: I love serving these plain, just as a bar cookie, or topping with ice cream!


Serving: 1bar | Calories: 322kcal | Carbohydrates: 40g | Protein: 6g | Fat: 16g | Saturated Fat: 7g | Polyunsaturated Fat: 2g | Monounsaturated Fat: 4g | Trans Fat: 1g | Cholesterol: 28mg | Sodium: 146mg | Potassium: 126mg | Fiber: 2g | Sugar: 28g | Vitamin A: 194IU | Vitamin C: 1mg | Calcium: 48mg | Iron: 1mg