Oatmeal Monster Brownies

18 Servings
Prep Time 10 minutes
Cook Time 35 minutes
Total Time 45 minutes

Oatmeal Monster Brownies are made with a layer of chewy oatmeal cookies with M&Ms, peanut butter chips, and semisweet chips, on top of fudgy brownies.

This easy and fun Brownie Recipe is based around delicious Monster Cookies. You get all the same fun mix-in ingredients found in the cookies, but with an additional layer of rich, chocolatey brownies.

Oatmeal Monster Brownies in stack


There’s nothing like a batch of brownies fresh out of the oven for the perfect family-size dessert! This version takes Classic Brownies and adds a fun layer of monster cookie dough over the top. So, you get all the best flavors from chewy monster cookies and fudgy brownies.

Oatmeal Monster Brownies prep steps, batter in baking dish, bowl of oatmeal topping, and topping being applied to brownies

If you haven’t had them before, monster cookies are like a mashup of a few popular cookie recipes. With a chewy oatmeal base, chocolate chips, M&Ms, and peanut butter flavor, you get a little bit of everything, and they’re an instant family favorite!

Oatmeal Monster Brownies in baking dish

If you’ve been following along for a while you probably remember Monster Brownies, which takes the mix-ins from our favorite monster cookie recipe and simply adds them to brownies. The difference with Monster Cookie Brownies is that we’ve also added the oatmeal cookie dough and not just the mix-ins. Every bite is like a combination of a cookie and a brownie for the ultimate sweet treat!



  • Prep time: Start the dessert recipe off by preheating your oven and spraying a 9×13 inch baking dish with non-stick cooking spray, so that they’re ready to go when the dough is done. 
  • Oatmeal Monster Cookie Dough: Add the old-fashioned oats, brown sugar, softened butter, flour, and baking soda to a large mixing bowl. Whisk the dough together until just combined. Then fold in the chocolate chip, peanut butter chip, and M&M mix-ins. 
  • Brownie layer: Add water to a medium saucepan and bring it to a boil. Turn off the heat before you add in the butter and cocoa powder. Whisk until the chocolate mixture is well blended, then pour it into a large mixing bowl. Mix in the granulated sugar, eggs, and vanilla extract until the batter is creamy. Sift in the dry ingredients and mix until just combined, but be careful not to overmix the batter. 
  • Baking time: Pour the brownie batter into the prepared baking dish and use an offset spatula to spread it out evenly. Then spread the oatmeal cookie dough over the top. Bake for 35-40 minutes until the brownies are set and the cookie dough is a beautiful golden brown color. Let the bars cool completely before slicing into squares.

Oatmeal Monster Brownies on cutting board


  • Chocolate chips: You can use different chocolate chips besides semi-sweet chocolate chips depending on your preference. Try using milk chocolate, dark chocolate, or white chocolate chips to change up the chocolatey flavor. 
  • Mix-ins: There are plenty of other delicious mix-ins you can add to the cookie layer. Reese’s Pieces, peanut M&Ms, toffee bits, pretzel pieces, or chopped nuts would all make tasty and fun additions.
  • Peanut Butter Brownies: For a fun twist on this recipe, you can make Peanut Butter Brownies for the brownie layer in the recipe. 



  • Serve: After baking the Monster Cookie Bars, they’ll be good at room temperature for 1-2 days. Cover baking pan in plastic wrap or foil to keep them moist. 
  • Store: You can also cover them or put them in an airtight container to store in the fridge for up to 1 week. 
  • Freeze: To freeze the brownies, slice them into squares and put them in an airtight container with the layers separated by parchment paper. They should stay good frozen for up to 3 months.

Oatmeal Monster Brownies on cutting board

Pin this recipe now to remember it later

Pin Recipe

Oatmeal Monster Brownies

Oatmeal Monster Brownies are made with a layer of chewy oatmeal cookies with M&Ms, peanut butter chips, and semisweet chips, on top of fudgy brownies.
Yield 18 Servings
Prep Time 10 minutes
Cook Time 35 minutes
Total Time 45 minutes
Course Dessert
Cuisine American
Author Sabrina Snyder


Oatmeal Monster Cookie Layer:

  • 1 1/2 cups quick-cooking oats
  • 1/2 cup brown sugar , packed
  • 1/2 cup butter , melted
  • 1/2 cup flour
  • 1/2 teaspoon baking soda
  • 1/2 cup semi-sweet chocolate chips
  • 1/2 cup peanut butter chips
  • 1/2 cup M&M candies

Brownie Layer:

  • 1/2 cup water
  • 2/3 cup unsalted butter
  • 3/4 cup unsweetened cocoa powder
  • 2 cups sugar
  • 2 large eggs
  • 1 teaspoon vanilla extract
  • 1 1/2 cups flour
  • 1/2 teaspoon baking soda
  • 1/4 teaspoon salt


Oatmeal Monster Cookie Layer:

  • In a large bowl whisk together oats, brown sugar, butter, flour, and baking soda until well combined.
  • Stir in chocolate chips, peanut butter chips, and M&M candies.

Brownie Layer:

  • Preheat oven to 350 degrees and spray a 9x13 baking dish with baking spray.
  • To a saucepan bring water to a boil.
  • Turn off the heat, add in the butter and cocoa powder.
  • Whisk until completely blended.
  • Pour mixture into a large mixing bowl.
  • Whisk in the sugar, eggs, and vanilla extract until creamy.
  • Add flour, baking soda, and salt until just combined.
  • Pour into the baking dish and spread evenly.
  • Spread Oatmeal chip dough over the brownie batter evenly.
  • Bake for 35-40 minutes.
  • Cool completely before slicing.


Calories: 390kcal | Carbohydrates: 55g | Protein: 5g | Fat: 18g | Saturated Fat: 11g | Trans Fat: 1g | Cholesterol: 54mg | Sodium: 164mg | Potassium: 142mg | Fiber: 3g | Sugar: 36g | Vitamin A: 413IU | Vitamin C: 1mg | Calcium: 32mg | Iron: 2mg
Keyword: Oatmeal Monster Brownies

Oatmeal Monster Brownies collage

About the Author: Sabrina Snyder

Sabrina is a professionally trained Private Chef of over 10 years with ServSafe Manager certification in food safety. She creates all the recipes here on Dinner, then Dessert, fueled in no small part by her love for bacon.

Sabrina Snyder is a professionally trained personal and private chef of over 10 years who is the creator and developer of all the recipes on Dinner, then Dessert.

She is also the author of the cookbook Dinner, then Dessert – Satisfying Meals Using Only 3, 5 or 7 Ingredients, published by Harper Collins.

She started Dinner, then Dessert as a business in her office as a lunch service for her coworkers who admired her lunches before going to culinary school and becoming a full time personal chef and private chef.

As a personal chef Sabrina would cook for families one day a week and cook their entire week of dinners. All grocery shopping, cooking and cleaning was done along with instructions on reheating. As a private chef she cooked for private parties and cooked in family homes in the evenings for families on a nightly basis after working as a personal chef during the day.

Sabrina has been certified as a ServSafe Manager since 2007 and was a longstanding member of the USPCA Personal Chef Association including being on the board of the Washington DC Chapter of Chefs in the US Personal Chef Association when they won Chapter of the year.

As a member of the community of food website creators Sabrina Snyder has spoken at many conferences regarding her experiences as a food writer including the Indulge Food Conference, Everything Food Conference, Haven Food Conference and IACP Annual Food Professionals Conference.

Sabrina lives with her family in sunny California.

Dinner, then Dessert, Inc. owns the copyright on all images and text and does not allow for its original recipes and pictures to be reproduced anywhere other than at this site unless authorization is given. If you enjoyed the recipe and would like to publish it on your own site, please re-write it in your own words, and link back to my site and recipe page. Read my disclosure and copyright policy. This post may contain affiliate links.


Leave a comment & rating

Your email address will not be published. Required fields are marked *

Recipe Rating

This site uses Akismet to reduce spam. Learn how your comment data is processed.