Turn your favorite cookie into cookie bars! These Monster Cookie Bars are loaded with peanut butter, chewy oats, chocolate chips, and mini M&M candies. These cookie bars are so simple to make, and are ready in no time!
One of my family’s all-time favorite cookies is monster cookies! These are made often in our house in different forms. We loved monster cookies that are formed into individual cookies and baked, I tried making a small batch in the air fryer, and these cookie bars require the least time to make.
These cookie bars combine all of my favorite flavors in one pan, and I don’t need to portion them out using a cookie scoop or anything. They are perfect to make and enjoy throughout the week (and enjoy with coffee!), I also love making them to parties and potlucks!
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Why You Will Love This Recipe
- Family Favorite. These cookies are loved by everyone in my family. Kids and adults love it alike.
- Convenient. You don’t need to portion out, roll and bake a dozen cookies here! Press the dough in the pan, bake, and slice!
- Gluten-Free Option Tested. I have tested this recipe with wheat all-purpose flour, and with gluten-free flour and both versions turn out great.
Key Ingredients
Complete list of ingredients with quantities and instructions is located in the recipe card below
- Flour. You need regular all-purpose flour to make these cookie bars, this flour is called “plain flour” in the UK. You can also use all-purpose gluten-free flour here.
- Baking Soda. Make sure that your baking soda did not expire! Add fourth a teaspoon to a bowl, then drizzle with vinegar or lemon juice on top of it, if it fizzes then it’s good to go. If not, then it’s time to get a fresh box.
- Butter, Egg, and Sugars. I use unsalted butter that is softened to room temperature, a large egg that is also at room temperature, and a mix of granulated white sugar and brown sugar.
- Peanut Butter. You can use creamy or chunky peanut butter here. I used smooth Skippy peanut butter.
- Oats. Quick or old-fashioned rolled oats work well here, I personally prefer rolled oats because they give you a chewy texture.
- M&M’s and Chocolate Chips. I used mini chocolate M&M candies, and a mix of regular semi-sweet chocolate chips (for the cookie dough), and mini chocolate chips (for the top).
How To Make Monster Cookie Bars
Before you do anything, preheat the oven to 375°F/190°C. Line a 9×9 inch pan with parchment paper or spray it generously with baking spray.
- Mix Dry Ingredients. In a bowl, combine the dry ingredients (flour, oats, baking soda, and salt). Set aside.
- Cream Butter and Sugar. In a separate bowl, cream butter with the sugars until creamy. That will take about one minute on medium speed using a hand mixer. Add the egg, vanilla extract, and peanut butter and beat again until creamy (1 more minute).
- Combine. Add the dry ingredients to the wet ingredients, and at the lowest speed possible whip until just combined. Don’t overmix as we don’t want to develop any gluten here.
- Press the Cookie Dough. Fold in the chocolate chips and M&M’s, then spread the cookie dough in the pan with a spatula. Smoothen the top with a spatula or greased hands, then sprinkle a few more M&M candies and mini chocolate chips.
- Bake. Bake in the oven for 15 minutes, or until the top of the cookie bar is no longer shiny.
- Allow to Cool. Cool completely on a wire rack in the pan. Then slice and serve.
Top Tips
Change it up! These cookies are loaded with peanut butter, oats, M&M’s, and chocolate chips. Want to add more good stuff? Why not! Add roasted peanuts, Reese’s pieces, raisins, butterscotch chips, cinnamon chips, or whatever your heart desires.
Size. I use a medium cookie scoop to make 20 cookies in total, if you use a small cookie scoop you will get 32 small cookies. Or use a large cookie scoop to make monster size cookies!
Don’t Overbake. These monster cookies are meant to be soft and chewy at the same time. If you overbake them, they can turn crispy and hard and that’s not what we’re looking for. So keep an eye on the cookies as they bake, they are ready when they are barely set in the center.
Storing & Freezing
Store in an airtight container for up to 4 days at room temperature. Or store in the fridge for up to 7 days.
These monster cookies freeze very well! There are two ways to freeze them:
- Freeze Unbaked. I like to use disposable square pans, press the cookie dough, place in a large Ziploc bag and freeze it until solid. Freeze for up to 2 months. When ready to bake, just remove it from the Ziploc bag and bake from frozen, you may need to add 2 extra minutes of baking time.
- Freeze Baked. After the cookies are baked and cooled completely, slice them into cookie bars and place in a Ziploc bag, and freeze for up to 1 month. Before serving, let them sit at room temperature for 30 minutes or microwave for a few seconds.
More Cookie Bars to Try
FAQs
If you haven’t heard of monster cookies before, they got their name because they are LOADED with all the good stuff!
Rolled large flake oats are my favorite to use in these cookies because they make them chewy. If you have quick oats and want to use them, you can, but the cookie bars won’t be as chewy.
I use mini chocolate M&M’s, they’re my first choice. But brownie, caramel, Christmas-themed, or mini M&M’s work.
Yes, just make sure that you use 1:1 gluten-free flour blend and gluten-free certified oats.
I hope that you love these monster cookie bars as much as I do! If you try this recipe, please share your experience in the recipe box below. I love hearing from you!
Monster Cookie Bars
Equipment
Ingredients
- ½ cup unsalted butter at room temperature
- ½ cup light brown sugar lightly packed
- ¼ cup granulated sugar
- 1 large egg at room temperature
- ⅔ cup creamy peanut butter not natural-style
- 1 teaspoon pure vanilla extract
- 1¼ cups all-purpose flour
- ½ teaspoon baking soda
- ¾ cup old-fashioned rolled oats
- ½ cup mini M&Ms plus extra for the top
- ½ cup semi-sweet chocolate chips
- 2 tablespoons mini semi-sweet chocolate chips for the top
Instructions
- Preheat the oven at 375°F/190°C. Line a 9×9 inch pan with parchment paper or spray it generously with baking spray.
- In a bowl, combine the dry ingredients (flour, oats, baking soda, and salt). Set aside.
- In a separate bowl, cream butter with the sugars until creamy. That will take about one minute on medium speed using a hand mixer. Add the egg, vanilla extract, and peanut butter and beat again until creamy (1 more minute).
- Add the dry ingredients to the wet ingredients, and at the lowest speed possible whip until just combined. Don't overmix as we don't want to develop any gluten here.
- Fold in the chocolate chips and M&M's, then spread the cookie dough in the pan with a spatula. Smoothen the top with a spatula or greased hands, then sprinkle a few more M&M candies and mini chocolate chips.
- Bake in the oven for 15 minutes, or until the top of the cookie bar is no longer shiny.
- Cool completely on a wire rack in the pan. Then slice and serve.
Notes
- Freeze Unbaked. I like to use disposable square pans, press the cookie dough, place in a large Ziploc bag and freeze it until solid. Freeze for up to 2 months. When ready to bake, just remove it from the Ziploc bag and bake from frozen, you may need to add 2 extra minutes of baking time.
- Freeze Baked. After the cookies are baked and cooled completely, slice them into cookie bars and place in a Ziploc bag, and freeze for up to 1 month. Before serving, let them sit at room temperature for 30 minutes or microwave for a few seconds.
Nutrition
This website provides approximate nutrition information for convenience and as a courtesy only. Nutrition data is gathered primarily from the USDA Food Composition Database, whenever available, or otherwise other online calculators.
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