Go Back
+ servings
three monster cookie bars stacked on a blue plate.
Print Recipe
4.80 from 15 votes

Monster Cookie Bars Recipe

Soft, chewy and full of peanut butter, oatmeal, chocolate chips and M&M's, these easy one bowl bars are always a favorite!
Prep Time10 minutes
Cook Time20 minutes
Cooling Time1 hour
Total Time1 hour 30 minutes
Course: Dessert
Cuisine: American
Servings: 32
Author: Lydia @ ThriftyFrugalMom.com

Ingredients

  • 3/4 cups butter, softened
  • 3/4 cup white sugar
  • 3/4 cup brown sugar
  • 4 large eggs
  • 2 cups creamy peanut butter
  • 2 1/2 tsp. baking soda
  • 5 cups quick oats
  • 1 1/2 cups chocolate chips (9 oz.)
  • 1 cup M&Ms

Instructions

  • Cream butter and sugars together. Add eggs and beat until fluffy.
  • Add remaining ingredients except for chocolate chips and M&M's. Mix well.
  • Fold in the chocolate chips and M&M's.
  • Firmly spread into a greased cookie sheet, smoothing the top into an even layer. (see Notes below) Bake at 350 for 17 to 20 minutes. Do not overbake! They will not be firm when done but should look baked on the tops and edges.
  • Let bars cool in the pan for around an hour, then cut into squares. If you do not let them cool completely, they will not hold together well.

Notes

Cookie Sheet Size: The pan size should be 13 in. x 18 in. in size.
Natural Peanut Butter: These bars have not been tested with natural peanut butter made only with peanuts and oil. So I can not guarantee that will work well in this recipe.
Use a 9x13 pan: If you prefer, you can halve the recipe and make it in a 9x13 pan. You may need to lessen the baking time though as well.
No M&M’s? You can use more chocolate chips instead!