Monster Cookie Bars are so easy to make, and full of delicious flavor. Such a fun treat to bake with the kiddos!

close up of four monster cookie bars with the a bite missing out of the top one

These are the bar version of my Monster Cookies. Cookie Bars are a great recipe for a first time baker. You can get things a little bit wrong (too much flour, not soft enough butter, etc) and still end up with a great dessert. Most cookie recipes that follow a 1 inch dough ball and yield around 30 cookies can be baked in a 9 by 13 inch pan for about 25 to 30 minutes.

a stack of four monster cookie bar recipe on a black rimmed tray

What are Monster Bars

The reason for the name Monster Cookies, or in this case Monster Bars, is because we are taking every kind of cookie and combining them. They are a hodge podge wonder dessert! These cookies contain:

M&Ms
Oatmeal
Chocolate Chips
Peanut Butter

Baking Tips and Tricks

Though cookie bars are very forgiving, I think they still present a great opportunity to teach our kiddos baking basics.

Measure the flour correctly. Your best bet is to weight the flour, but if you don’t have a kitchen scale, you will want to scoop it with a spoon into a dry measuring cup. Read all about this here: How to Measure Flour.
Cream the butter and sugar together well. Beating them together helps add air to the butter, which yields light and fluffy cookies. Make sure you beat them together for about 3 to 6 minutes.
Use fresh ingredients. Fresh baking soda and baking powder are critical to baking. Each needs to be replaced about every six months. You can test their freshness by dropping baking soda in a little vinegar or baking powder in a little water. They should bubble immediately.

top down look at four monster cookie bars with chocolate chips and M&Ms in them.

Storing and Freezing

After allowing the bars to cool completely, store them in an airtight container for up to 1 week.

Alternatively, freeze on a parchment lined baking sheet for 1 hour and then transfer to an airtight container. Freeze for up to three months.

These are actually incredibly delicious right from the freezer.

front on view of four monster cooke bars stacked with a milk glass with striped straws in the background

Other Great Cookie Bars

If you can’t get over cookie bar recipes, make these with the kids!

If you love these cookie bars or make others, please leave me a comment and let me know what you think!

4.75 from 8 votes

Monster Cookie Bars

Serves: bars

(tap # to scale)

Prep: 20

Cook: 27

Total: 47

Monster Cookie Bars are so easy to make, and full of delicious flavor. Such a fun treat to bake with the kiddos!

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Ingredients

1 cup all purpose flour see note 1 (120 grams)
1/2 teaspoon baking soda
1/2 teaspoon baking powder
1/4 teaspoon salt
1 cup unsalted butter room temperature (226 grams)
1 cup brown sugar packed (213 grams)
1/2 cup granulated sugar (198 grams)
1 1/2 cups creamy peanut butter (405 grams)
2 large eggs room temperature
2 teaspoons vanilla extract
1 cup milk chocolate chips (170 grams)
1 cup M&Ms (170 grams)
1 cup quick cooking oats or old fashioned, see note 2 (89 grams)

Instructions

Preheat your oven to 350 degrees Fahrenheit. Spray a 9 by 13 inch baking dish with cooking spray and set aside.
In a medium sized bowl, whisk together the flour, baking soda, baking powder, and salt until fully combined. Set aside.
1 cup all purpose flour, 1/2 teaspoon baking soda, 1/2 teaspoon baking powder, 1/4 teaspoon salt
In a large bowl with a hand mixer (or in a stand mixer fit with the paddle attachment) beat together the butter, brown sugar and granulated sugar, until light and fluffy. About three minutes. Then proceed to beat in the peanut butter until fully combined.
1 cup unsalted butter, 1 cup brown sugar, 1/2 cup granulated sugar, 1 1/2 cups creamy peanut butter
Beat the eggs into the butter/sugar/peanut butter mixture, one at a time. Finally, beat in the vanilla.
2 large eggs, 2 teaspoons vanilla extract
Add in the flour mixture all at once (see note 3) mixing it in on a very low speed until it just begins to combine and then up the speed just a little and mix in until the flour has just disappeared.
Finally, stir in the chocolate chips, M&Ms, and oats.
Dish the batter into the baking pan. It will be very sticky. Spray a spatula with cooking spray and use that to spread out the dough.
Bake for 25 to 27 minutes or until the edges of the bars are golden brown. Allow to cool completely before cutting into 24 equal squares.
Store in an airtight container for up to 1 week. See notes in the post about freezing.

Notes

To measure the flour, spoon it into the measuring cup and level off the top, rather than scooping it right from the flour container.
Both quick cooking and old fashioned oats (often sold as rolled oats) both work in this recipe. Just use what you have on hand. Keep in mind it will change the texture just a little bit because quick cooking oats are old fashioned oats broken down. It’s just a matter of personal preference.
Most cookie recipes suggest that you mix in the flour a little at a time so that the flour does not fly everywhere and it suggest that you not over-mix. I recently read that you should add it all at once, mixing in slowly at first so it doesn’t go everywhere, and then just mixing until the flour disappears. This lowers the risk of over stimulating the gluten which can lead to a dense cookie.

Nutrition Information

Author: Lisa Longley

Course: Dessert

Cuisine: American