These Halloween Monster cookie bars are gooey and rich with peanut butter, oats, and Halloween M&M candies. Perfect for spooky season or a Halloween party.
Gooey Halloween Monster Cookie Bars
With spooky season upon us, it’s only fitting that we make monster cookies. These Halloween Monster Cookie Bars are a perfect treat for your next Halloween party or cozy Fall day in drinking apple cider.
A few features of this recipe that make it great:
- Thick and gooey cookie bars that are crisp along the edges.
- Full of mix-ins like peanut butter, oats, chocolate, and M&Ms.
- Easy-to-make recipe — you can make the dough in one bowl with no mixer needed.
- Perfect for parties and sharing.
For some other great Halloween desserts I’d also recommend checking out Pumpkin Snickerdoodle Bars and Halloween Chocolate Sprinkle Cookies.
What are Monster Cookie Bars?
Monster cookie bars are essentially a traditional monster cookie baked in a square pan instead of scooped into individual cookies. Which then probably brings up the real question which is what is a monster cookie? Well, my friend, I don’t know why they are called monster cookies lol but I presume it’s because they either are usually large and kinda ugly looking, or because they’re filled with so much stuff.
These monster cookie bars have all of the same ingredients as monster cookies, with ratios and instructions adjusted for baking in a square dish. I like to slightly underbake them for extra gooey middles hehe.
Ingredients for Halloween Monster Cookie Bars
- Melted, unsalted butter
- You could also use browned butter, but if you do start with 9 tbsp instead of ½ cup.
- Creamy Peanut Butter: Something like Jif or Skippy peanut butter work best. Avoid natural or chunky peanut butters.
- All-Purpose Flour: Be sure to measure flour correctly. A scale will work best, otherwise use the scoop-and-level method.
- Old Fashioned Oats: These are also known as rolled oats. Make sure you are not using steel cut or quick oats, as those have a different texture.
- Light Brown Sugar and Granulated Sugar: For sweetness.
- Egg + Egg Yolk, room temperature: Soak eggs in a bowl of hot water for 5-10 minutes to bring them to room temperature.
- Ground Cinnamon: Adds depth and Fall spice to the flavors.
- Halloween M&Ms: Use the Ghoul’s Mix M&Ms to make these spooky season themed, but you can swap out any other color for the different seasons.
- Dark or Semi-Sweet Chocolate Chips: I like using dark chocolate chips (60%+ cacao) since I the flavors are deeper and less-sweet, but use your favorite.
- You could try chopping up a chocolate bar as well.
- Optional Candy Eyes: These are purely for decorative purposes but they look like little monster eyes and we love that.
How to Make Halloween Monster Cookie Bars
Step 1: Whisk warm melted butter and peanut butter together smooth. Then whisk in the sugars, egg, egg yolk, and vanilla until you have a smooth and creamy mixture.
Step 2: Combine the dry ingredients — flour, baking soda, salt, and rolled oats in a separate bowl to form an even mixture. Fold the flour into the wet ingredients until the flour is almost fully combined.
Step 3: Add the M&Ms and chocolate chips and fold until evenly distributed.
Step 4: Press the dough into an 8×8 inch square baking pan. Sprinkle some additional M&Ms and chocolate chips on top of the dough before baking.
Step 5: Bake the monster cookie bars for 23-25 minutes, or until the edges are golden and middle is puffed up with not completely done. Press some candy eyes on top and sprinkle with flaky sea salt after baking if you desire. Then allow the bars to cool for at least 30 minutes before enjoying.
Tips for Halloween Monster Cookie Bars
- Do not over-bake the bars: You truly do not want to bake these for too long, otherwise they will dry out and become crumbly. One way to make sure that they are cooked enough is to check that the top if puffed up and no longer super glossy. It’s okay if the center is not fully set, you just don’t want it to be visibly raw.
- Line greased pan with parchment paper: Lining the pan with a strip of parchment paper that hangs 1-2 inches over the sides makes it easy to lift the bars out of the pan when they are done.
- Use a metal baking pan: Using a metal pan ensures an even bake. Glass pans heat the bottom and edges a lot faster than the middle, meaning those could end up over-baked while the center is still raw.
Add-In Ideas
If theory holds that these are they are called monster cookies due to the sheet amount of add-ins, then why not add even more or swap a few out? Here are a few of my favorite add-in or substitutions.
- Add chopped up pretzels or nuts to add crunch and some sweet and salty flavors.
- Substitute the peanut butter with cookie butter to change up the flavor.
- Swap M&Ms for Reese’s Pieces or Peanut Butter M&Ms.
- Change out the M&M colors depending on the season.
Pin & Save for Later
Are you interested in making this recipe but aren’t ready to bake yet? You can actually save this recipe to Pinterest by hovering over (or tapping on mobile) any image in this post. It’ll be waiting for you when you’re ready.
Hope you enjoy your Halloween Monster Cookie Bars!
Gooey Halloween Monster Cookie Bars
These Halloween Monster Cookie Bars are the perfect spooky season treat. They're gooey with peanut butter, oats, and Hallowen M&Ms.
Ingredients
- ½ cup creamy peanut butter, like Jif or Skippy
- ½ cup melted butter
- ½ cup light brown sugar
- ½ cup granulated sugar
- 1 large egg
- 2 tsp vanilla extract
- 1 cup all purpose flour
- 1 cup old fashioned oats
- ½ tsp baking soda
- ½ tsp ground cinnamon
- ¾ tsp salt
- ¾ cup Ghoul Mix M&Ms
- ¾ cup chocolate chips
- Candy eyes for decorating
- Flaky sea salt
Instructions
- Preheat the oven to 350°F and then grease an 8x8 inch square pan and line it with a strip of parchment along the sides and bottom. The parchment will help you lift the bars out of the pan.
- In a mixing bowl, whisk the melted butter and creamy peanut butter together until smooth.
- Add the granulated sugar, light brown sugar, egg, and vanilla and whisk until the mixture is smooth and creamy.
- In a separate bowl, combine the flour, oats, baking soda, ground cinnamon, and salt. Add this to the bowl of wet ingredients and gently fold everything together until the flour is almost fully combined.
- Add the chocolate chips and M&Ms and fold until the add-ins and evenly distributed and flour is mixed in. Do not over-mix the dough.
- Spread the dough into the baking pan to form and even layer. Feel free to top it with some more M&Ms and chocolate chips.
- Bake the bars for 28-32 minutes, until the edges are golden and set and middle is puffed up and no longer shiny. It's okay if the middle isn't fully set as it will continue cooking as the bars cool. Do not over bake the bars or else they will be dry.
- Press some candy eyes into the bars (if desired) after they come out of the oven.
- Let the bars cool for at least 30 minutes in the pan before lifting them out of the pan and cutting into slices. They'll still be warm, so for a cleaner cut let them cool down completely first.
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