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+ servings
Stack of three monster cookie bars
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5 from 3 votes

Monster Cookie Bars

Monster Cookie Bars ~ Soft, chewy bars stuffed full of peanut butter chips and M&M's!
Prep Time10 mins
Cook Time15 mins
Total Time25 mins
Course: Dessert
Cuisine: American
Servings: 20
Calories: 532kcal
Author: Julie Evink


  • 1/2 c. butter softened
  • 3 eggs beaten
  • 1 c. white sugar
  • 1 tsp vanilla
  • 1 tsp corn syrup
  • 2 tsp baking soda
  • 1 c. brown sugar
  • 1 1/2 c. peanut butter
  • 4 1/2 c. quick oatmeal
  • 6 oz. chocolate chips
  • 6 oz M&M's


  • 1. Mix butter and sugars together.
  • 2. Add eggs, vanilla, corn syrup, and baking soda. Sir in peanut butter. Stir in oatmeal. Add chocolate chips and M&M's
  • 3. Bake in a greased 13×18 inch pan at 350 degrees for 15 minutes for a soft, chewy bar. They will not look done, but will cook as they set.



Tips and Tricks for the BEST Monster Cookie Bars!
  • You only need one bowl to make the cookie dough, but be sure to add the ingredients in the order listed! 
  • Start with room temperature butter.
  • Be sure to use quick oats for this recipe. If you don't have quick oats, you can break down old fashioned oats in a food processor and they will work fine. Just pulse them a few times.
  • When you press the dough into the pan press it just enough so it's in the pan, but not too hard otherwise your cookies will be too dense.
  • The cookies don't have to bake long and they won't look done when you pull them out of the oven, which is what you want for soft and chewy cookies. They will continue to bake and set up as they rest in the pan.
  • Wait until the cookie bars are completely cooled before you slice them. The cookies may fall apart if you slice them while they're warm.
  • Once your Monster Cookies are completely cooled you can slice them and store them in an airtight container.
  • These cookie bars will keep well at room temperature for up to three days as long as you keep them tightly wrapped or in an airtight container. Or, you can keep them in the refrigerator for up to a week. They won't be as soft if they're cold, so leave them out at room temperature before serving them.
  • Yes, you can freeze these Monster Cookie Bars! First, make sure the cookies are cooled before freezing them. Transfer them to an airtight container and freeze them for up to three months. To thaw, just leave them out at room temperature.
  • If you want to switch things up try using milk chocolate chips or dark chocolate chips. Or, add some white chocolate chips! You can also use chopped up chocolate candy like peanut butter cups or Heath bars in place of the M&Ms. If you love nuts, try adding some chopped walnuts, pecans or almonds.


Calories: 532kcal | Carbohydrates: 72g | Protein: 16g | Fat: 22g | Saturated Fat: 9g | Cholesterol: 38mg | Sodium: 298mg | Potassium: 356mg | Fiber: 6g | Sugar: 33g | Vitamin A: 185IU | Calcium: 56mg | Iron: 3mg