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These Monster Cookie Bars take my most popular monster cookie recipe and turn it into an easy, no-scoop dessert you bake right in a 9×13 pan. They’re thick and chewy peanut butter oatmeal bars loaded with M&M’s and chocolate chips, with crisp golden edges and a soft, gooey center. If you love monster cookies but don’t want to scoop and bake batch after batch, these monster bars are for you. They are made in one bowl and feed a crowd.
These Monster Cookie Bars take everything you love about classic monster cookies and bake it right in a 9×13 pan. They’re thick, chewy peanut butter oatmeal bars loaded with M&M’s and chocolate chips, with crisp golden edges and a soft, gooey center. No scooping, no batch after batch of cookie sheets. Just press, bake, and slice.
My Monster Cookies are one of the most popular recipes on Modern Honey, and my family asks for them constantly. But let’s be honest, scooping four dozen cookies takes time. So I turned them into bars, and now I make these for bake sales, potlucks, and those nights when someone needs a treat right now.
The dough comes together in one bowl, bakes in about 22 minutes, and yields 24 big bars per pan.
Make them for any holiday just by changing the color of the M&M’s. If you love monster cookies, check out my Christmas Monster Cookies because they are always a hit during the holidays. If you love gluten-free recipes, check out my Gluten Free Monster Cookies.
Why you will love these Monster Cookie Bars
- No scooping. You press the dough into one pan instead of baking batch after batch.
- Crisp edges, gooey center. You get the texture of a perfect monster cookie in every square.
- One bowl. Cleanup is easy.
- Feeds a crowd. One 9×13 pan makes 24 bars, and you can double it in a half-sheet pan.
- Freezer friendly. Bake a pan now and save some for later.
Ingredients:
- Butter – Creamed with the sugars to create a soft, rich base for the bars.
- Brown Sugar and Sugar – Brown sugar adds moisture and a deeper, caramel-like flavor, while granulated sugar balances sweetness and helps with texture.
- Peanut Butter – The signature flavor of monster cookies! I recommend using a thick peanut butter like Jiffy or Skippy. Not natural peanut butter because it separates and has a different oil and sugar content, which can throw off the texture and make the bars greasy or affect how they set.
- Eggs – Bind the ingredients together and add structure and moisture to the bars.
- Vanilla Extract – Use a high-quality vanilla.
- Rolled Oats – Give these bars their classic hearty, chewy monster cookie texture.
- Flour – Provides structure to hold the bars together.
- Baking Soda – Helps the bars rise just enough while baking.
- Salt – Balances the sweetness and enhances the other flavors.
- M&M’s and Chocolate Chips – The classic monster cookie mix-ins, adding color, crunch, and pockets of melty chocolate throughout every bar.
Can I use natural peanut butter in this recipe?
It’s best to avoid natural peanut butter here. It tends to separate and has a different oil-to-solid ratio than processed peanut butter like Jif or Skippy, which can make the bars greasy or change the way they set up. Stick with a classic, shelf-stable creamy peanut butter for the best texture.
How to make the Best Monster Cookie Bars:
- Prep the pan. Preheat the oven to 350°F. Line a 9×13-inch pan with parchment paper, leaving some overhang on the sides so you can lift the bars out, and lightly spray it with nonstick spray. A light-colored metal pan works best.
- Cream the butter and sugars. Beat the softened butter, brown sugar, and sugar for 2 to 3 minutes, until light and fluffy.
- Add the peanut butter, eggs, and vanilla. Mix in the peanut butter until smooth, then add the eggs one at a time and the vanilla.
- Add the dry ingredients. Add the oats, flour, baking soda, and salt. Mix on low just until combined.
- Fold in the mix-ins. Stir in the M&M’s and chocolate chips, saving about ½ cup of M&M’s for the top.
- Press into the pan. Spread the dough evenly into the pan, pressing it all the way into the corners, and smooth the top. Press the reserved M&M’s into the top so they look pretty after baking.
- Bake. Bake for 22 to 28 minutes. Start checking at 22 minutes. They’re done when the edges are golden and set, the top is lightly golden, and the center looks just barely set and slightly soft. A toothpick in the center should come out with moist crumbs, not wet batter. If the edges are browning too fast before the center is done, loosely cover the pan with foil for the last 5 to 10 minutes.
- Cool completely. Let the bars cool in the pan for at least 1½ to 2 hours before cutting. They’ll finish setting as they cool, and cutting too early makes them fall apart.
- Cut and serve. Lift the bars out using the parchment and cut into 24 bars.
Baking Tips!
Tent with foil if needed. If the edges are browning too fast, loosely cover the pan with foil for the last 5 to 10 minutes of baking.
Don’t skip the cooling time. These bars need at least 1½ to 2 hours to fully set, even though it’s tempting to cut into them right away.
Use a light-colored metal pan. Dark pans absorb more heat and can cause the edges to overbake before the center is done.
Check early. Start checking for doneness at 22 minutes, since ovens vary and these bars go from perfectly chewy to overbaked quickly.
How to tell when they are done baking:
The edges should be golden brown and pulling slightly from the sides of the pan. The center should look set and no longer shiny, but still soft when lightly pressed. A toothpick in the center should come out with a few moist crumbs, not wet dough. If you wait until the center looks fully done, the bars will be dry once they cool.
How to cut clean bars:
Lift the whole slab out with the parchment. Use a large, sharp knife and press straight down instead of sawing, wiping the blade between cuts. Chilling the bars for 20 minutes first gives the cleanest edges. I also like to use a plastic knife because it cuts cleaner.
Frequently Asked Questions:
- Can I use quick oats instead of rolled oats? Rolled oats give the best chewy texture, but quick oats can be substituted, though the bars may have a slightly less chewy texture.
- Why do my bars fall apart when I cut them? This usually means they haven’t cooled long enough. Let the bars cool completely in the pan for at least 1 hour before cutting for clean slices.
- Can I use crunchy peanut butter instead of creamy? Yes, crunchy peanut butter will work and will add a bit of extra texture, though creamy gives the smoothest, most classic result.
- Can I swap the M&M’s or chocolate chips for other mix-ins? Absolutely — peanut butter chips, white chocolate chips, or other candy pieces can be substituted or added in place of the M&M’s and chocolate chips.
- Can I freeze these bars? Yes, once fully cooled, these bars freeze well. Wrap individually or layer with parchment paper in an airtight container and freeze for up to 3 months.
Storage:
Store bars in an airtight container at room temperature for up to 3-4 days. For longer storage, freeze in an airtight container for up to 3 months and thaw at room temperature before serving.
Cookie Dessert Bars:
My classic peanut butter cookie recipe is soooo soft and chewy with crisp edges! If you’re a chocolate lover, make my chocolate bottom peanut butter cookies. Also, check out my Peanut Butter Blossoms Cookies and Reeses Chocolate Peanut Butter Cup Cookies.
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Monster Cookie Bars
Ingredients
- 1 cup Unsalted Butter (softened)
- 1 cup Brown Sugar
- 1 cup Sugar
- 1 cup Creamy Peanut Butter (Skippy's or Jif)
- 2 large Eggs
- 2 teaspoons Vanilla Extract
- 1 1/2 cups Rolled Oats (or quick oats)
- 2 cups Flour
- 1 teaspoon Baking Soda
- 1/2 teaspoon Salt
- 2 cups Plain M&M’s
- 1 1/2 cups Chocolate Chips
Instructions
- Preheat the oven to 350°F. Line a 9×13-inch pan with parchment paper, leaving some overhang on the sides so you can lift the bars out, and lightly spray it with nonstick spray. A light-colored metal pan works best.
- Beat the softened butter, brown sugar, and sugar for 2 to 3 minutes, until light and fluffy.
- Add the peanut butter, eggs, and vanilla. Mix in the peanut butter until smooth, then add the eggs one at a time and the vanilla.
- Add the oats, flour, baking soda, and salt. Mix on low just until combined.
- Stir in the M&M’s and chocolate chips, saving about ½ cup of M&M’s for the top.
- Spread the dough evenly into the pan, pressing it all the way into the corners, and smooth the top. Press the reserved M&M’s into the top so they look pretty after baking.
- Bake for 22 to 28 minutes. Start checking at 22 minutes. They’re done when the edges are golden and set, the top is lightly golden, and the center looks just barely set and slightly soft. A toothpick in the center should come out with moist crumbs, not wet batter. If the edges are browning too fast before the center is done, loosely cover the pan with foil for the last 5 to 10 minutes.
- Cool completely. Let the bars cool in the pan for at least 1½ to 2 hours before cutting. They’ll finish setting as they cool, and cutting too early makes them fall apart.
- Cut and serve. Lift the bars out using the parchment and cut into 24 bars.
Notes
- Don’t overbake. Pull the bars when the edges are golden and the center looks just set. They firm up as they cool.
- Peanut butter: Use a creamy, no-stir brand. Do not use natural peanut butter.
- Gluten-free: Use certified gluten-free oats and gluten-free flour.
- Aluminum Pan: I suggest using a metal aluminum pan rather than a glass pan. Glass pans bake differently (harder edges and undercooked centers).
- Cutting: Cool completely, or chill 20 minutes, for clean slices.
- Storage: Keep airtight at room temperature up to 4 days, or freeze up to 3 months.
Nutrition
Nutrition information is automatically calculated, so should only be used as an approximation.
